Djokovic denies Davydenko at the O2

Defending champion Novak Djokovic produced a gutsy performance to clinch a 3-6 6-4 7-5 victory over Nikolay Davydenko in Monday night's Group B clash at the Barclays ATP World Tour Finals in London.

After Rafael Nadal's defeat by Robin Soderling at the O2 Arena earlier it looked like another upset was on the cards when Davydenko took the first set but the world number three dug deep to come through in a match lasting nearly three hours.

Djokovic came into the tournament as arguably the man to beat after back-to-back titles in Basle and Paris. Indeed, his only defeat since the US Open came in the semi-finals of the Shanghai Masters last month - to Davydenko, who went on to beat Nadal in the final.

This was also a repeat of last year's final - again played in Shanghai - where the Serbian prevailed in straight sets.

The opening exchanges were predictably tight, both players looking at home on the indoor surface, but it was the ultra-consistent Russian who broke through first in the fifth game.

Davydenko, who is playing in the end-of-season tournament for the fifth year in a row, then saved two break points to cement his advantage.

Suddenly Djokovic was making errors, and a double fault and wild forehand put Davydenko in sight of another break, this time to seal the set, which he duly achieved thanks to a return that dropped on to the line.

Djokovic was desperate for an early breakthrough in the second set but Davydenko refused to crack and the third seed's frustration got the better of him in the third game as he hurled his racquet to the ground.

A couple of rare unforced errors from the world number seven in his next service game presented Djokovic with two break points but the Serbian could only dump successive returns tamely into the net.

Djokovic trudged back to his chair with his head bowed, perhaps starting to feel the exertions of the past six weeks.

Djokovic is a renowned fighter, though, and he redoubled his efforts in the ninth game, engineering a break point and then taking it when a Davydenko forehand just missed the line.

The crowd, which for the first time in the tournament featured plenty of empty seats, appreciated his efforts and the noise level rocketed when the world number three saved a break point before levelling the match with an unreturnable forehand.

Djokovic then made the perfect start to the decider, breaking Davydenko in the opening game. The Serbian was looking increasingly weary, though, and he was forced to save three break points in a titanic sixth game.

The finish line just would not come and, serving for the match, Djokovic was finally broken, his opponent nailing a backhand down the line.

But, having worked so hard for his break, Davydenko promptly gave the initiative back with a woeful service game and second time around, with the clock approaching midnight, Djokovic finally sealed victory.