Highlights - Federer beats Nadal in London
By Piers Newbery
BBC Sport at the O2 Arena
Roger Federer won the season-ending title for the fifth time and laid down a marker for 2011 with a three-set victory over world number one Rafael Nadal in London.
The 29-year-old's attacking game carried the Swiss to a 6-3 3-6 6-1 win in one hour and 37 minutes at the O2 Arena.
Federer's victory ensured that an inconsistent year by his standards was bookended by wins at the Australian Open in January and now the ATP World Tour Finals in November.
Nadal had been hoping to land the only significant title to so far elude him but a three-hour semi-final against Andy Murray on Saturday looked to have taken the edge off his game, and Federer proved the stronger in the closing stages.
And while Sunday's final never quite matched the heights of their last meeting in London - Nadal's epic 2008 Wimbledon final victory - it proved beyond doubt that Federer will be chasing hard on the world number one's heels next year.
Federer, who picked up a cheque for just over $1m for his week's work, said: "I've really enjoyed playing here, it's been a wonderful atmosphere once again. Rafa's had an amazing year, one any player dreams of."
While Nadal admitted he had been outplayed. "I want to congratulate Roger," he said. "He played unbelievable throughout the whole week. It was a fantastic year for me, probably the most emotional of my career."
The last time the top two players in the world contested the year-end final was 24 years ago, when Ivan Lendl beat Boris Becker in New York, and few match-ups in history can have prompted such excitement as Federer and Nadal's six-year rivalry.
Diego Maradona had been an ever-present figure at the O2 all week but on Sunday he was joined by the likes of Thierry Henry, Ronnie Wood, Kevin Spacey and Princess Beatrice among the capacity 17,500 spectators.
Home favourite Murray might have been despatched in three epic sets by Nadal on Saturday, but the Spaniard's 22nd meeting with Federer was a more than fitting finale for this or any other season.
While Federer was appearing in his sixth year-end final, having won four times, the 24-year-old Nadal was making his debut and looking to claim the one title of note that had remained absent from his CV.
Last year's disastrous week in London, during which Nadal failed to win a single set, was long forgotten after an unbeaten run through the group stages this time around and a 14-7 head-to-head record more than countered the two defeats by Federer in their only indoor meetings, the last of which was three years ago.
It was Federer who started the better, though, moving as effortlessly as he had all week and keeping Nadal off balance with some smart serving out wide to the Spaniard's backhand.
Nadal has the consolation of ending the year as the world number one
A sharp backhand volley and flowing cross-court backhand winner had the crowd roaring in game five, and Federer moved ahead with a beautiful forehand down the line and a sweeping backhand winner to break serve for 5-3.
The set was wrapped up in ruthless fashion after just 32 minutes and there was the feeling that Nadal might at last be flagging in the early games of the second set.
Surprisingly, it was Federer who opened the door as his first-serve percentage plummeted, and a couple of loose volleys and a wayward forehand gave Nadal the break at 3-1 in the second set.
With Federer now going through a lull, Nadal took full advantage by powering through his next three service games to level the match and force the decider that most observers had hoped for.
An absorbing match had yet to really catch fire as we waited for both men to hit top form at the same time, but it was Federer who took the initiative in the final set by recovering from 40-15 down in game four to break, after another killer drop volley and two forehand errors from Nadal.
A nervous service game followed for the Swiss but again that wide serve to the Nadal backhand with the pace taken off got him out of trouble at 30-30, and once that danger had passed Federer powered towards the finish line.
Another break of serve followed as a tired-looking Nadal netted successive backhands and Federer sealed the victory with a looping forehand, before clearly enjoying the rapturous reception as he reclaimed the title he last won in 2007.