Novak Djokovic enhanced his reputation as World No.1 with a straight sets win over Roger Federer to win the ATP World Tour Finals after a thrilling contest at the O2 Arena in London.

Djokovic recovered from a break down in the first set to win the tiebreak 8-6, and then from double set point down in the second to claim a lucky 13th career victory over six-time champion Federer.

The final crowned a fitting winner in the unbeaten Djokovic, whose father was admitted to hospital a fortnight ago with reported respiratory problems, and worked as a epic finale to a thrilling 2012 season which had seen four different grand slam winners amid one of the most exciting year's in the men's game

Novak Djokovic
Djokovic claimed his third win of 2012 against Federer in thrilling fashion.

The final match of the season saw the top two players in the world meet for a fifth time, with Federer, who beat US Open champion Andy Murray in the semi-final, seeking a record seventh title and Djokovic, the victor against Juan Martin del Portro in the last four, looking to claim his first since 2008.

In front of a hostile crowd more akin to a Davis Cup tie than an ATP event, Federer, already a winner in London at Wimbledon in July, immediately looked the more comfortable, reeling off nine points in a row to take the early break.

The 17-time grand slam champion was clearly keen to keep the points short, but as Djokovic opted to sit deep, the errors began to come from the Federer forehand, and upon finding the net in the fifth game, the Serbian took full advantage of a wayward backhand.

What followed was among the highest quality tennis seen on the tour in 2012, as blow after blow was exchanged by the two heavyweights of men's tennis.

Djokovic appeared to have struck the knock-out blow in the set in the ninth game when after spurning two break point chances with two wide service returns, he benefited as Federer, aiming to become the oldest winner of the season ending championship, netted inexplicably.

But the roller-coaster nature of the duos' rivalry has always allowed for the unexpected and despite facing a set point at 40-30, Federer saw Djokovic net a regulation forehand before the No.2 seed forced back the Australian Open champion to yield an error.

Federer guaranteed himself at least a tiebreak with a hold to 15, but treatment to Djokovic's elbow, which delayed the start of the 12th game only work to swell the tension in Greenwich.

The Serbian held serve to set up a tiebreak in which the two players couldn't be separated until a long Federer forehand forced a second set point for Djokovic.

Roger Federer
Federer lost his second final in London.

An enthralling rally ended with Federer producing a passing forehand winner, but Djokovic wasn't to be denied, and won two consecutive points to take the opening set 7-6.

But if the world No.1 thought the opening set would open the floodgates he was to be mistaken as Federer repeated his feat from the opening set, breaking early for a 2-0 lead.

The six-time grand slam champion had little in reply however, and was almost down a double break, facing a seventh break point of the match at 3-1, but a wide Federer forehand kept Djokovic in contention.

And his resilience almost brought a break back of his own as, with the ball keeping lower, Federer netted a backhand, only to produce an ace when required.

Another Federer error gave Djokovic a further opportunity to break, however a deep forehand was followed by the deftest of volleys as the defending champion again dug deep.

It was the turn of Djokovic to show some resilience when Federer created two set points at 5-4, but he first sent a forehand into the tramlines and then hit another forehand beyond the baseline.

Having taken the game to deuce, Djokovic put together back-to-back points, forming a rigid defence against an onslaught from Federer, to break for 5-5.

He ensured himself of a tiebreak with a splendid service game to pile the pressure on Federer who wilted under the strain, sending a passing backhand wide, before a brilliant backhand down the line on Championship point brought a fitting finale to a thrilling contest and gifting Djokovic his 74th win of 2012 and a second end of the season title of his career.