Novak Djokovic won his third consecutive ATP World Tour Finals title on a walkover after Roger Federer pulled out ahead of the match.

The world No 2 fought for almost three hours to defeat countryman Stan Wawrinka in the semi-finals on Saturday night, saving four match points, and did not leave the O2 Arena until the early hours of Sunday morning.

There was speculation Federer may again have been feeling his back and that only increased when he failed to show up for a scheduled practice session on Sunday afternoon.

The announcement was made following the doubles final, which was won by Bob and Mike Bryan, with Federer taking to the court to explain the situation to the fans.

He said: "Unfortunately I'm not match fit to play match tonight. Clearly I wish it wasn't this way. You try all year to be ready for the ATP World Tour Finals and I didn't want to end this way.

"I tried everything I could last night and today - painkillers, rest - until the very end, but I can't compete at this level with Novak. In a final like this and at my age, it would be too risky. I hope you understand."

The news was a huge disappointment for the sell-out crowd, with the clash between the world's top two a highly-anticipated occasion, but they accepted it with little dissent.

And the mood picked up when they were told the match would be replaced by an exhibition clash between Djokovic and Andy Murray, which the world No 1 won 8-5.

Federer's withdrawal meant Djokovic became the first player since Ivan Lendl in the 1980s to win three consecutive World Tour Finals titles, with the Serbian unbeaten at the O2 since 2011.

Djoko shocked

The top seed had heard nothing of Federer's troubles until he was told his opponent had withdrawn during the doubles final.

Addressing the crowd, Djokovic said: "Clearly this is not the way I wanted things to happen. I'm really sorry for Roger not being able to come to the court.

"I've known him for a long time and I would say he and Rafa (Nadal) are the biggest competitors, guys who always give 100 per cent, so I'm sure, if he could have come out and played, he would have done.

"I wish him all the best to recover. He has an important week ahead of him.

"I feel disappointed for you guys. This is probably the first time in history something like this has happened and I apologise for that. I'm glad Andy's here and I hope we can put on a good show."

The hollow victory brought Djokovic his seventh title of the season and extended the gap between the two at the top of the rankings.

"It's very hard to talk about the achievement of this trophy," said Djokovic. "I'm not one of those players that celebrates these wins.

"But this trophy is the crown for all the achievements of this year. I'm very happy to be able to stand here and finish with this trophy."

Fans will be contacted within the next 48 hours and should receive a partial refund as well as priority for next year's final.
(Sky Sports)