Novak Djokovic underlined his world No. 1 ranking with a dramatic victory over Roger Federer to win the ATP World Tour Finals.
In a fitting finale to the season, the world's best two players thrilled the crowds at the O2 Arena, with the Serb eventually emerging triumphant with a 7-6(6) 7-5 victory to claim a second year-end title.
Djokovic was not at his best for much of the match, but battled from behind in both sets to deny Federer a third successive victory in London.
Djokovic, who deposed Federer at the top of the world rankings last week, was punished for a sluggish start by the Swiss, who burst out of the blocks with an early break.
Federer, who had to battle past Andy Murray in the semi-finals, fired an early statement of intent, kicking off the match with an ace as he romped through his opening service game to love. By contrast, Djokovic started with a double fault and was broken to love as he was helpless to prevent Federer racing to a 3-0 lead.
It was a tentative start from Djokovic, but he began to find his range, and despite being on the back foot for much of the early exchanges, broke back to claw his way back into the opening set.
With Djokovic in the ascendancy Federer swiftly quashed any hopes Djokovic had of winning a fourth successive game to streak to victory in the opening set.
Despite being some way off his best, Djokovic kept chipping away and after Federer saved two break points at 4-4, but he was unable to fend off a third as the Swiss dumped a forehand into the net as Djokovic got his nose in front for the first time.
But in a topsy-turvy opening set, Federer broke straight back as the opening set headed for a tiebreak. Djokovic won just 27 per cent of points on his second serve, but he dug deep to clinch the opening set.
As the pair battled for the ascendancy in a lengthy opening game of the second set, Federer once again started the set the better, converting a fourth break point to keep his hopes of victory firmly alive.
The Wimbledon champion had the chance to grab a double break and all but secure the second set, but his forehand failed him as Djokovic somehow contrived to hang on once again.
As the match edged closer to the two-hour mark, Djokovic's chance to break back appeared to have gone begging when the ball sat up off the top of the net, only for the Serb to flash wide as Federer held on for a 5-3 lead.
Just as it looked like the match was heading for a decider, a magnificently crafted drop shot from Federer proved to be in vain as Djokovic forced his opponent to serve for the set. The 31-year-old saw two set points pass him by as Djokovic roared back to level.
Playing with a steely determination, Djokovic then held his serve, and in a remarkable turnaround Federer was now serving to stay in the match. A pair of sloppy strokes from Federer handed Djokovic match point, and a sensational backhand winner proved a fitting end to a dramatic contest.