Last Updated: 05/01/13 5:05pm
And that's it! Southampton had taken the lead early on, but that seems like a very, very long time ago now. It's a dream double on debut for Demba Ba as Chelsea keep their title defence well and truly on track. Well, I hope you've enjoyed it. I'm Ryan Gordon wishing you a great rest of your weekend. Cheers all!
Marko Marin shows plenty of intent as he runs at his marker out wide before getting past him and breaking to the by-line, but he just overruns it and can't pull his cross back as the ball goes behind for a goal-kick.
Almost a second for Frank Lampard now as Demba Ba is able to skip through before squaring the ball to his team-mate in the area, but the England international can't control and gifts the ball back to the defenders.
Both sides look content to run out the last few minutes, with several mis-placed passes flying all over the place at the moment.
The fourth official raises his board and shows there will be four minutes of added time for the Saints to get through here at the end of the game.
A booking in the closing stages for James Ward-Prowse as he recklessly brings down Oscar in the middle of the park.
David Luiz gets on the end of the delivery to produce a powerful header, but it's straight at Boruc who plucks the ball out of the air.
The Southampton fans are already filing out of the stadium, but the Chelsea fans aren't going anywhere and are in fine voice. They want more here this afternoon, and they might just get some.
It's very harsh penalty on Southampton as Frank Lampard's lifted pass hits the chest of Maya Yoshida, but the referee adjudges the defender to have handled the ball, with Chelsea's veteran midfielder stepping up to fire home from the spot.
Ten minutes plus stoppages left here at St Mary's, and Nigel Adkins will probably just be hoping the score-line doesn't tilt even more in the visitors' favour before the end.
First booking of the afternoon now as Steve de Ridder sees yellow after bringing Eden Hazard down from behind.
Southampton must know they're beaten here, but they don't look like they're ready to give up at the moment and are starting to build-up a bit of steam.
Down at the other end and Boruc sticks out a vital leg to prevent Demba Ba from notching up his hat-trick with a far-post header.
It's just not Southampton's day. Puncheon drives down the wing before whipping his delivery in, with Ward-Prowse controlling at the far-post only to see his drive saved point-blank by Turnbull, who quickly gets himself up to send Schneiderlin's follow-up shot over.
I've lost count of the number of passes the Blues have put together just in the last 60 seconds, but a long switched pass to Eden Hazard brings that run to an end as he can't keep the ball from going out for a throw.
It looks like it's going to be a long final 30 minutes or so for Southampton, who are being outplayed in every area of the park at the moment.
Chelsea change now, with Frank Lampard getting a run-out, with Branislav Ivanovic making way. Attacking midfielder on for a centre-back? Rafael Benitez is clearly after more goals this afternoon.
More woes for Southampton now as defender Jose Fonte needs to be stretchered off, with Jos Hooiveld coming on in his place.
Far too easy for Chelsea now as they effectively put this tie to bed. Ramires passes to Eden Hazard on the edge of the area, with the playmaker simply playing the ball on to the near-post run of Demba Ba, whose first-time shot creeps under the goalkeeper and into the back of the net.
Really promising move for the hosts now as Rodriguez times his run perfectly to get in behind the defence, but Do Prado's through-ball is far too heavy and the striker can't keep the ball in play when Ward-Prowse had been waiting unmarked in the area.
Almost a fourth for the Blues now as Artur Boruc can only tip a deep delivery into the path Eden Hazard, but Luke Shaw does brilliantly to get his body in front of the ball before turning the striker and taking the ball out of defence.
Chelsea don't have to wait long for their third though as Juan Mata strolls down the wing without a defender in sight before clipping a wonderful ball into the area where Branislav Ivanovic towers above his marker before sending a textbook header down and into the back of the net.
Mata has a dig from a good 25-yards out, although his curling effort is deflected behind for a corner. The delivery is a really dangerous one and flashes across the six-yard area, but no blue shirt can get the on the end of it and the defenders clear.
Demba Ba looks to turn provider as he breaks down the wing before playing the ball along the edge of the area to pick out the unmarked Juan Mata, but he shows a rare lapse in concentration as he mis-controls the ball to allow the defence to win back possession.
Juan Mata looks to slide Eden Hazard through on goal, but the Spaniard gets just too much on his pass as the ball runs out for a goal-kick.
No changes from either side at the break to tell you about as both managers are apparently satisfied with the respective XI out there.
With Chelsea now in the lead, Sky Bet have the Blues a comfortable 1/6 to hold out for the win, a Southampton come-back victory at 16/1, while a draw will get you 5/1.
Fine finish from Victor Moses as he gives Chelsea the lead right on the stroke of half-time. Ashley Cole creates it, breaking into the area from out wide before cutting the ball back to his team-mate who takes one touch to control before rifling his shot low past the keeper. It's Southampton 1, Chelsea 2 at the break, so join me soon for the second-half at St Mary's.
Less-than-spectacular from Demba Ba now as he looks to pull off an insanely technical volley, but he gets it all wrong and blazes his effort out for a throw.
The fourth official shows there will be two minutes of time added on here at the end of the first-half. Eden Hazard is limping now though after another penetrating run into the area, and the medical staff will be eager to get him into the tunnel to undergo some treatment.
Meanwhile, Ba creates himself a great chance after controlling Ramires' cross in the area, but the striker stumbles on the turn and allows Boruc to just get out and smother the danger.
Frank Lampard is doing some laps down on the touch-line and looks to be as eager as ever to get out there with his team.
Eden Hazard looks really dangerous for Chelsea when coming forward, and he again breaks down the wing with purpose before looking to get the ball into the area, but his cut-back is too angular and evades all his awaiting Chelsea team-mates.
Guilherme do Prado has a pop at goal at the other end, but his effort is tame and Turnbull makes a comfortable save.
That goal seems to have knocked some of the stuffing out of the hosts, and Chelsea are enjoying an extended spell of possession around the opposition area. Victor Moses has a fierce drive at goal after controlling a cross with his chest, but it's straight at the goalkeeper, who shouldn't be beaten from there anyway.
Chelsea are level, and it's a debut goal for Demba Ba! Ramires' delightful flick plays Eden Hazard down the wing, with the playmaker feeding the ball on to Juan Mata, who cuts passed his marker before seeing his clipped shot just saved by the fingertips of Artur Boruc, but Ba is there to slam the loose ball into the roof of the net.
Former Chelsea youngster Jack Cork gets right up alongside Ashely Cole as the defender is pressured to clear, and the Saints man does really well to keep the England international pegged in before winning his side a throw.
Ramires drives at the defence and gets past two men before winning the Blues a corner. It's taken short but wasted as the Saints rob possession, but Ramires gets back really well to nip the ball off Ward-Prowse to end a potentially dangerous counter.
Southampton break once more but Puncheon takes just a second too long to get his slide pass away to the over-lapping Steven Davis, who just checks his run as the pass is released, with the ball eventually rolling out for a goal-kick.
Corner at the other end now, but Gary Cahill's header comes off the head of a defender and out for another corner. This one is not as dangerous though and Artur Boruc can easily collect.
Corner for the Saints now which is whipped in deep before falling to Schneiderlin on the edge of the area, but after sending his marker one way his shot is blocked by a crowd of bodies and the Blues can eventually clear their lines.
Terrific attempt from Hazard now as he picks up the ball on the angle of the area before looking to curl his effort into the far-post, but he just doesn't get his angles right and the ball trickles wide of the up-right.
Chelsea almost respond instantly as Demba Ba gets past the last man before running clean through on goal, but the referee adjudged the striker to have fouled Fonte, although replays suggest the Senegal international didn't do much wrong.
It felt like a goal was coming, and there it is. Southampton break really well, with Jay Rodriguez apparently just far too quick for Gary Cahill, who can hardly keep up with the striker as he runs through before clipping a sumptuous effort past Turnbull and into the back of the net.
Good tempo to this game now, with both sides looking confident when going forward. It's still goalless though, but there seems to be more intent from the front men.
Rodriguez thinks he's in behind the defence and controls a long ball with his chest before turning to shoot, but he was at least two yards off-side and the linesman's flag snaps up to signal as much.
Ramires picks up the ball on the left-wing and trots inside before looking to slide Ba in behind the defence, but he can't get the right weight on his delivery and the ball skips through to the goalkeeper.
Luke Shaw does well to get past one man on the wing before winning a throw-in off another, but his quickly-taken delivery is not where the ball went out and a good chance to catch the Blues napping goes begging.
The Southampton man needs to go off for some treatment, but he's immediately back on the field and ready to soldier on.
Chelsea create a really dangerous looking move as Hazard breaks through the middle of the park before rolling the ball out wide to Ramires, but they lose possession on the edge of the area and Southampton a break with some really sharp passing, with Steven Davis eventually being felled in the middle of the park.
Demba Ba threatens for the first time this afternoon as he ghosts past his marker before cutting the ball back from the by-line, but it's straight to Jose Fonte who clears easily.
Jack Cork receives the ball on the wing before looking to run at the heart of the Chelsea defence, but the ball gets caught up under his feet and he's forced to turn and play the other way.
Good pressing from the Saints now as they force Ashley Cole to go all the way back to his goalkeeper, with little in the way of options in the midfield.
Ramires and Juan Mata link up wonderfully on the edge of the area, with the latter winning his side a corner. The delivery is pretty decent by the defenders just manage to flick the ball away, while David Luiz eventually blazes a shot miles over after the ball had been put back into the danger zone.
Very sloppy from David Luiz as he passes the ball straight out of play when under zero pressure from the Southampton forward men.
A decent piece of defending from Ivanovic as he outmuscles Rodriguez before just getting a toe on the ball to prevent the striker from running through on goal following a quick break by the hosts.
Chelsea finally get hold of the ball and Juan Mata tries to thread it through for Eden Hazard, but there's too much on the pass and the defence can nip in and win back possession.
The Saints are enjoying pretty much all of the ball in the opening minutes, and even when they give it away they get it straight back, although all of this is happening in the middle of the park.
After a brief delay for some photographs of the respective captains, referees and match delegates, this third-round tie is up and running!
The teams head out into what is a spring-like afternoon in Southampton, and it's only the pre-match formalities that stand between now and the kick-off.
Callum, from Essex, writes in: Hope to see Chelsea win comfortably today, pleased to see Ba in the line up as well. I'm predicting 3-0 Chelsea, Mata, Moses & Ba all on the score sheet.
We're around 10 minutes away from the kick-off now and the two sets of players are busy lining up in the tunnel. Mike Dean is the man in charge today and should be leading the teams out momentarily. St Mary's, by the way, is absolutely buzzing...
We've got our first caller of the day, with a supremely confident Blues fan, Andrew from Watford, emailing: Chelsea 6-0 today! Ba hat trick, Ivanovic Cahill and Moses.
For Southampton, James Ward-Prowse and Jay Rodriguez both return to the side as Nigel Adkins largely keeps his faith in the XI that drew against Arsenal in midweek.
So, big news in the Chelsea line-up then as new £7million signing Demba Ba comes straight into the starting XI at the expense of Fernando Torres. That makes one of six changes to the side that lost to QPR, with Ashley Cole captaining the side while Ramires, Juan Mata and Eden Hazard also return, while Frank Lampard and El Nino are relegated to the bench.
Southampton: Boruc, Cork, Fonte, Yoshida, Shaw, Puncheon, Steven Davis, Schneiderlin, Ward-Prowse, Do Prado, Rodriguez Subs: Kelvin Davis, Hooiveld, Lambert, Lee, Mayuka, Reeves, De Ridder
Chelsea: Turnbull, Azpilicueta, Ivanovic, Cahill, Cole, Ramires, Luiz, Mata, Hazard, Moses, Ba Subs: Hilario, Lampard, Torres, Oscar, Ferreira, Marin, Bertrand
The team sheets have just come across my desk, but first here's your chance to get involved by emailing your thoughts or predictions to firstname.lastname@example.org and I'll share them with our other readers right here.
This one, then, seems to be set up quite nicely, but why not make it a little more interesting by popping over to our friends at Sky Bet, who have Southampton at 9/2 for the win today, while Chelsea are at 4/7 to progress to the next round.
Chelsea do, however, head into the tie on the back of a very surprising 1-0 defeat to Premier League basement sitters Queens Park Rangers, while they will also be looking for a much improved title defence in this competition, having already seen their Champions League crown snatched away after failing at the group stage.
Nigel Adkins's side could do with another fairytale at St Mary's this afternoon as the manager searches for a way to lift the side's spirits and hoist them away from the bottom-four. A win over the west London giants would go a long way in doing just that, but the hosts will be under no illusions as to the task they face today.
Some 13 places separate top-four Chelsea and relegation threatened Southampton in the Premier League, but it is the Saints who have history on their side in the FA Cup, with the Blues having failed to win any of their last seven against today's opponents.