Last Updated: 18/04/12 9:38pm
Barca try a last-gasp push as Pedro hits the post then his ball rebounds out to Busquets, who fires wildly into the stands.
What a save from Cech! Puyol's glancing header from a Messi free-kick feeds Thiago, who pokes the ball goalwards from close range but the keeper just manages to keep it out.
The ball just won't come down for Kalou, fed by Drogba in the Barca box and a late chance goes begging for Chelsea.
Xavi lofts in a cross from the right meant for Thiago but Ivanovic gets his head to it first to clear.
Barca are building with slightly more urgency as the minutes trickle down. Kalou does brilliantly to get the ball away from Messi near the Chelsea box.
Great work from Drogba as he breaks on the counter-attack but his pass to the goal-bound Kalou is a fraction too long.
We're into the final 10 minutes at Stamford Bridge and Barcelona are still seeking an equaliser. Alves' cross is deflected away to Xavi but he can't split the Chelsea defence with his shot.
Alves takes a long run up and fires his kick straight into the Chelsea wall in a repeat of Messi's earlier effort.
Terry tangles with Messi after he slips away from Meireles and it's another free-kick for Barca, this time from further out.
Mascherano fires a great long pass out to Alves on the right but his attempted cross into the box is cleared by the Blues backline.
Barca are on the ball in the Blues half trying to find a way through, but Cole blocks Pedro's attempted cross out on the right.
Drogba seems to have recovered after his groin trouble. Chelsea are preparing to make their first change as Kalou gets to his feet.
Lampard's resulting long free-kick floats in towards Terry but he can only get a glancing header to it and it doesn't trouble Valdes.
Xavi steps up to take this one and manages to clear the wall but also clears the crossbar as he fires his shot high.
Ramires is hit with the first booking of the night and Barca have a free-kick from an even better position than the last.
Play resumes and Drogba is back on his feet but limping a bit. Messi is caught by Ramires on the edge of the penalty box.
Drogba is on the floor again after trying to win the ball from Puyol and appears to have picked up a groin injury.
Nothing comes of Xavi's corner as Mikel gets a touch to it in the box. Barca prepare to make a change...
The hosts fail to make the most of the free-kick as Barcelona snatch back possession. Messi makes another break but his shot is deflected behind by Terry for a Barca corner.
Messi drives his delivery straight into the Chelsea wall and Lampard keeps it in over on the right. The Blues break and Drogba wins a free-kick off Mascherano in midfield.
Mikel commits a handball a few yards outside the Chelsea box and he concedes a free-kick from a dangerous position.
Messi makes the home side sweat as he skips off on one of his trademark runs from midfield but the Blues defence manage to shut him down.
Sanchez releases Xavi with a clever backheel as they team up down the right but Ramires intervenes for the hosts.
A good run from Cole down the left puts Barca under more pressure but Alves manages to diffuse the threat.
Mata floats in a Chelsea free-kick from distance and Barca are given the advantage after Cahill appears to handball.
Mascherano makes an important and well-timed challenge on Lampard on the edge of the penalty area to halt the midfielder's goal-bound charge.
Barca keep pressing as Alves latches onto Adriano's cross across the face of goal but his shot is wildly off-target.
Sanchez fluffs his lines for Barca and Chelsea heave a sigh of relief. Fabregas scoops the ball over the Blues backline to his team-mate but he appears to hesitate under pressure in the box, allowing Cole to clear with a sliding challenge.
Sanchez escapes Cahill in the box but the defender recovers to win back the ball. Some solid defending from the centre-half so far this half.
Messi looks dangerous as he makes a break and forces a crucial clearance from Cahill. Alves fires in a low cross seconds later and it's Terry that intercepts.
The hosts win a throw in the middle of the park after some well-organised defending gets the ball away from Barca in the Blues half.
There's a chance as Lampard whips in a solid delivery and Cahill stretches but can't quite get on the end of it.
Barcelona have had a total of 12 attempts to Chelsea's three so far. The Blues win a throw in the Barca half and Cole's effort is headed behind by Alves for a corner.
Adriano gets away from Lampard and weaves towards goal, unleashing a powerful shot which Cech does well to palm away in a diving save.
Messi's corner is cleared by Lampard and goes straight out for a Barcelona throw as the visitors continue to push.
Barca win a corner as Iniesta tries a shot and it's deflected behind by Ivanovic. Messi steps up to take it.
Barcelona are probing once again, but Chelsea force them back into midfield to keep them at a safe distance.
It's pouring with rain in West London but it's not dampening the home crowd, who are still in good voice.
Cole does well to win the ball back in the Blues' half and pairs up with Ramires to get forward down the left.
Barca waste no time getting on the attack as Messi charges forward, trying to curl a shot around Cahill, but the Blues defence hold firm.
@Ladanafrah tweeted to say of Drogba - "despite his diving and the amount of time he spends on the floor. He actually brought credibility to the game. #Proud"
@carlosbriones99 doesn't expect Chelsea's lead to last for long. He tweeted - "barça is gonna make a comeback later and they're gonna win 3-1."
Steve the 'Passionate Gooner' says - "Chelsea will need to keep it tight at the back, they cannot afford to make any defensive errors, clearly they'll also need to keep a reign on Messi. Keep a clean sheet and if they can score a second that will put them in the driving seat."
@GeorgieHaikali tweeted - "drogba still showing what his capable of....im on chelsea's side today....come on blues."
Gabriel Sutton thinks Barca's patience could pay off - "I think Barcelona are playing a very patient game at the moment. Chelsea have done well to get the goal just before half time but I can see barca scoring an equalizer in the second half. They certainly won't panic. Verdict 1-1."
Jack Dry is glad Di Matteo left Torres on the bench - "Great match! Chelsea have been completely dominated but they have their crucial goal from who other than Didier Drogba who was picked over Fernando Torres. Good choice from di mateo."
Sam Thornton is backing the Blues to get another - "terrific goal from Chelsea I reckon we will score one more goal with lampard. Come in Chelsea!!!"
Gordon Phillips thinks Barca's class will shine through - "Anyone who loves football will hope that this wonderful Barcelona team will eventually make class tell. Chelsea have been a good impersonation of Stoke and if that's what you like........"
Darryl from Rochdale wrote in to say - "Thats what Drogba can do if he stops spending too much time rolling around on the floor."
To say he's been rolling around for much of that first half, Drogba did superbly with the finish to give Chelsea the advantage. The Blues held their own and got their reward - but can they do the same again after the break?
The whistle blows and it's Chelsea 1 Barcelona 0 at half-time! What did you all think of that? Tweet me @SkySportsRachG or email email@example.com.
A mistake from Messi, of all people, allows Ramires to break and he picks out Drogba with a pinpoint cross after a storming run, allowing the striker to drive home with a great finish.
It's Messi's turn to go down as he slips awkwardly but he's back on his feet seconds later. Barca are in possession as the seconds trickle down...
Drogba goes down in another heap as two minutes stoppage time are added this half, but nothing is given.
Messi tries to pick out Sanchez in the Chelsea box but hoofs his pass over his team-mate's head, prompting shouts of 'who are ya?' from the home faithful.
Heart-stopping moment there for Chelsea and vital last-gasp clearance from Cole. Messi tries another shot seconds later but mishits it.
Messi gets away from Mikel in midfield on a superb break and looks certain to score as he beats Cech but Cole is there to clear the ball almost off the line.
Xavi launches in the corner and Alves strikes the ball on the volley but sends it flying into the stands.
Cole charges down an Alves ball at the expense of a corner kick to Barcelona on the right of the Blues goal.
Meireles tries a shot on the volley from far out but it's blocked by Busquets. Five minutes to go in this half and Chelsea have handled themselves well so far.
Cole produces some nice footwork to feed Meireles and evade Xavi down the left, much to the home crowd's appreciation.
The ref hands a free-kick to Chelsea inside their own half, won by Mikel. Drogba goes down after an awkward landing, trying to win the ball against Busquets.
The skipper gets his wrist strapped up and the game resumes after a brief lull in play. Barca are back on the ball in the middle of the park.
Puyol is having a chat with the Barca bench about his apparent arm problem. Looks like a wrist knock and he receives some medical attention.
The ball is clipped into the Chelsea box and Puyol pounces, but accidentally hoofs Drogba in the face in the process and the Blues get the advantage.
Cole produces an important clearance to deny Alves as he advances on goal, beating Cech to the punch.
Didier Drogba feeds Ramires with a through ball but Puyol beats the Brazilian to it, despite looking in some discomfort with his arm seconds earlier.
It's all Barcelona at the minute as they build in their trademark style but Ivanovic spots a run from Iniesta and closes him down.
Torres is warming up on the touchline for Chelsea, who are in possession in their own half as Ivanovic and Terry exchange passes, getting a breather after that attack.
Cech makes a crucial low save as Messi clips a ball towards goal and Barca are turning up the heat now.
Fabregas beats Cahill to try a shot from the left and drives it in towards Cech but the keeper bends it away at the near post.
Didier Drogba produces some good footwork to try a break for the hosts but Alves catches up to him and dissolves the threat.
Xavi keeps Chelsea on their toes with a diagonal ball in towards Messi on the edge of the box but Cahill intervenes. Iniesta goes down in the box after an apparent push but the ref is unmoved.
The Blues enjoy some rare possession but another weak Meireles pass means Mata can only keep the ball in as it goes back to the visitors.
Mata leads a Chelsea break from the set piece but Meireles can't find Lampard with a poor delivery, allowing Mascherano to pounce.
After a build-up of teasing and probing, Barcelona win a corner on the left which Messi steps up to take.
At the other end, Cech charges out to close down another Barca attack. The tempo has definitely risen in these last couple of minutes.
Ramires and Mata put the Barca defence under pressure in the box and Chelsea win a throw. Ivanovic's long effort falls to Mata, who attempts a shot from long-range but it goes wide.
Woeful effort from Fabregas there. Cech does well to parry an Iniesta shot but it rebounds to the ex-Arsenal man, who lashes at it and fires wildly off-target from close range.
Messi finds space for a shot but is closed down by Mikel and Meireles. The visitors continue to apply the pressure but Fabregas misses a gaping chance.
Barca have had the most of the possession so far but Chelsea have stopped them from finding their usual rhythm in the early stages.
The Blues striker is pulled back to his feet by Puyol and there doesn't appear any damage done. The ball rolls back to Cech, who lofts upfield, but the flag goes up as Mata is called offiside.
Meireles has to be careful if he wants to avoid a booking now. Drogba is on the floor after claiming he's been caught by Busquets.
Barcelona are sitting comfortably on the ball as they exchange passes in midfield. Meireles slides in on Busquets for another Barca free-kick and gets a talking to from the ref.
Sanchez is on the ground, apparently hurt, after a collision with Terry in midfield but soon returns to his feet.
Cahill slips the ball towards Terry in the box and the captain slides in with a shot but can't quite force it over the line and it goes behind for an Valdes goal-kick.
Xavi's delivery goes straight into the waiting gloves of Cech. Chelsea get their first let-off of the night seconds later as Sanchez's strike towards an empty net pings off the crossbar.
Meireles charges in with a late tackle on Fabregas in the Chelsea half and Barca are handed a free-kick from long range on the left.
Drogba escapes Mascherano after some poor defending and breaks for the Blues but Puyol hunts the striker down.
Ivanovic tries to pick out Ramires with a long pass down the left of the Barca half but Alves is there to make a scuffed clearance, which falls to Xavi.
Busquets and Drogba tangle in the Chelsea half and the advantage goes to the visitors. Ramires goes down soon after but nothing is given.
Back on the ball, Barcelona return to their trademark passing game but Meireles intervenes for the hosts.
Ramires manages to run Messi off the ball, much to the delight of the home crowd. Drogba tries to chase down a long kick from Cech but it just gets away from him and rolls back to Valdes.
Fabregas gives the ball away to Chelsea for the first time but is caught late by Ivanovic and it goes back to the visitors.
We're underway at Stamford Bridge and the European champions get things rolling, trading passes in their own half.
The teams are out to a rocking reception from the Stamford Bridge crowd. Almost time for kick-off...
It's worth noting Barcelona have the small matter of their La Liga El Clasico to deal with this weekend as they bid to cut Real Madrid's lead at the top. Chelsea, meanwhile, travel to Arsenal top-four rivals Arsenal.
@HeroHussain tweeted - "Chelsea to win tonight! I have faith as a Chelsea supporter! Come on lads go on and tame the Catalan giants!"
Bob Baumann thinks Wilshere could be onto something - "Barcelona 1, Chelsea 0. Fabregas with the winner after a beautiful 3 pass combination inside the area. Xavi-Messi-Fabregas."
Alain Cabache, following the game all the way from Boston, USA, says - "Don't understand fans that are saying that Chelsea are going to do well and then predicting scores like 2-1 or 2-2. For Chelsea to do well they must first and foremost keep a clean sheet. Any Chelsea goals are a bonus, the more the better! If we do concede, then we must score 2 or 3 more than them. 2-1 or 2-2 are terrible scores to go to Nou Camp with. 3-0 to Chelsea."
Charlie Goldie wrote in - "I never knew that Pepe Guardiola's team have never won against Chelsea, good to know. I think the blues will win 2-1, Chelsea seem a whole new side under Di Matteo, and they have been impressive in Europe this season, I think they have to make the most of the first leg as they are at Stamford Bridge, I think Chelsea will keep their unbeaten record against Guardiola tonight."
@AdamBourne2 doesn't fancy Chelsea's chances. He tweeted - "Messi to score first and Barca to win 2 nil."
Cesc Fabregas' old team-mate Jack Wilshere has just tweeted - "I think Cesc would love to score tonight.....him and Lampard never liked each other on the pitch!" Will the former Arsenal skipper be on the scoresheet do you think?
The two sides have been well-matched in the competition in the past, playing each other 10 times, with each team winning three. The four other games were drawn.
Blues fan Ben thinks Chelsea can edge it this evening - "As a Chelsea fan, I believe we have to defend well and hopefully string some passes together and counter. 2-1 to Chelsea is my prediction with Drogba and Lampard (penalty) scoring and Messi scoring for Barca."
Dave Jessop wrote in - "Just been playing Football Manager and the Champions League Semi first leg in 2016 was Chelsea 0 Barca 1 - Could that be an omen? - going for 2-0 to Barca BTW."
@RowanElliott has tweeted to say - "I think Chelsea are going to surprise us all tonight! 2-2 final score."
Roberto Di Matteo's side will be out for revenge after they were knocked out at the same stage three years ago by the Catalan giants on away goals.
A quick stat for you - Chelsea are the only team that Pep Guardiola's Barcelona have played but never beaten.
Here's a betting update from our friends at Sky Bet on tonight's game - Chelsea have been well backed in the build-up to tonight's clash and are consequently cut from 4/1 to 7/2 with a draw 3/1 and Barcelona 7/10. Didier Drogba leads the line for the Blues, who are 7/2 to make the final, and is price boosted from 8/1 to 9/1 to open the scoring.
Barcelona: Valdes, Dani Alves, Puyol, Mascherano, Adriano, Busquets, Iniesta, Xavi, Messi, Sanchez, Fabregas. Subs: Pinto, Pique, Bartra, Thiago, Keita, Pedro.
Chelsea: Cech, Ivanovic, Cahill, Terry, Cole, Mikel, Lampard, Meireles, Ramires, Mata, Drogba. Subs: Turnbull, Essien, Torres, Malouda, Bosingwa, Kalou.
We'll be bringing you the team news very shortly but first why not drop us a line ahead of kick-off at 7.45? Email firstname.lastname@example.org or Tweet @SkySportsRachG.