Roger Federer will face Novak Djokovic in the final of the ATP World Tour Finals after prevailing in a three-set epic with Stanislas Wawrinka at the 02 Arena.

The 17-time Grand Slam champion had to save four match points against his Swiss counterpart in comfortably the most highly-contested match of the tournament.

Wawrinka became the first person to break Federer at this year's event in the third game of the opener, and his dominance from the baseline helped him to a second break which took him 5-2 ahead.

The world number two immediately responded with a break of his own, but Wawrinka had already establish a big enough cushion to close out the first set, having not dropped a point on his first serve.

The second set went with serve for the first 11 games, though it was the third seed who looked the most likely to break as he bludgeoned from the back of the court to put the Federer serve under duress.

However, a series of Wawrinka errors gifted Federer a break to love in the crucial 12th game as the 33-year-old levelled the encounter at a set apiece, having been holding on for much of the second.

Federer soon lost his momentum as a scoring mixup with the umpire contributed to him surrendering his serve in the opening game of the deciding set, and Wawrinka held until he was serving for victory.

The Australian Open champion served and volleyed twice on match point, but firstly miscued into the tape and then allowed Federer to make just his second forehand winner of the evening with a passing shot.

A remarkable forehand return and Wawrinka finding the net saw Federer break back at 5-5, and the Davis Cup teammates each held serve to take the thrilling contest to a dramatic final-set tiebreak.

Wawrinka failed to convert another two match points in the breaker and Federer kept coolest under pressure with two subtle drop shots at the net to claim a 4-6 7-5 7-6(8) victory which sets up a showdown with world number one Djokovic, who beat Kei Nishikori in London this afternoon.