Andy Murray's hopes at the ATP World Tour Finals suffered a blow on Wednesday as Novak Djokovic came from a set down to beat the British No 1 in a three-set thriller at the O2 Arena.
Having opened his campaign in London with victory over Tomas Berdych, Murray looked on course to make it two wins from two as he started in hugely impressive fashion to claim the first set against the World No 1.
But Djokovic raised his game to take the second and then prevailed in an enthralling, topsy-turvy decider to clinch a 4-6 6-3 7-5 triumph - improving his record against the Scot to 4-3 this season.
Murray made the ideal start as he broke his opponent in the opening game of the match, some typically diligent defensive work forcing a loose half-volley from Djokovic which the Scot was quickly on to dispatch.
Serving superbly, Murray remained strong on his own delivery and had the chance to close out the set at 5-3 on the Djokovic serve as he came back from 40-0 down to take his rival to deuce on three occasions, earning a set point in the process with a delightful drop-shot.
The Serb clung on to remain in touch, but Murray got the job done on his own serve in the next game, holding to love as Djokovic blazed a backhand long.
The home favourite had the chance to secure an early break in the third game of the second set as a net-chord took a Djokovic forehand wide, but the World No.1 saved it with a drive-volley that caught the baseline and duly survived.
Djokovic then brought up his first break point of the contest in the sixth game after some great scrambling at the net and made it count as Murray sent a volley fractionally long after charging the net.
It would prove a decisive move as he produced a couple of strong service games to level the match at one set apiece.
Having wrested the momentum from his opponent, Djokovic got his nose in front in the decider with a break in game three; Murray falling 0-40 down after dragging a backhand wide and then coming up with another error on the same wing to put his opponent in control.
The Scot looked to be wilting and was forced to fend off a break point in both of his next service games but, having done so, then appeared to summon new reserves as he broke back to level at 4-4 when a challenge correctly proved Djokovic had sent a backhand wide.
At that point the match looked like it could go either way, but Djokovic would secure an all-important break in game 11 as a retreating Murray put a forehand long and the Serb then survived two break-back points in the next to eventually serve out for the match.