David Goffin caused a semi-final upset at the ATP Finals on Sunday (AEDT) as he added the scalp of Roger Federer to that of Rafael Nadal.

Goffin did not look like repeating his win over Nadal early on at the O2 Arena but the Belgian surged back from a set down to triumph 2-6 6-3 6-4 and claim his first victory over world No.2 Federer.

Federer raced through the first set in just 33 minutes and, given his 6-0 record against Goffin, looked strong favourite to progress.

However, it was not to be. For the second day running, Goffin mounted a sensational comeback to set up a meeting with either Grigor Dimitrov or Jack Sock, while extending Federer's wait for a seventh title at the end-of-season event.

Five times Federer fashioned a break chance in the opening game and, although Goffin battled hard to save four, there was nothing he could do with the final one as the Swiss moved ahead, the No.7 seed sending a backhand well beyond the baseline.

The Wimbledon champion gained a double break in the fifth game thanks to two sublime backhands down the line, Federer's groundstrokes working like clockwork as he raced into a 4-1 lead.

He wasted his first set point as Goffin, playing with strapping on his left knee, battled bravely, but in Federer's fourth service game the 1-0 lead was secured, the 36-year-old comfortably holding to love.

Amazingly the anticipated march into the final failed to materialise as Goffin dug deep to level the match in style.

He raced into a 3-0 lead by breaking Federer in the second game, only the third time he has lost his serve during the tournament in London.

Federer did apply pressure on his opponent but all too often his previously perfect groundstrokes found the net, Goffin targeting the Swiss' forehand and enjoying some success.

Anyone who made Federer favourite in the decider was soon beginning to rue their decision as Goffin again upped his game, and his illustrious rival struggled to stay with him.

Game three proved pivotal as Goffin, who will lead Belgium at next weekend's Davis Cup final against France, found himself with two break chances.

Federer saved the first but could not halt Goffin's momentum and he took a 3-1 lead.

He then only dropped one point on serve to round out a memorable victory that ensures a surprise victor in London.

STATISTICAL BREAKDOWN
Goffin [7] bt Federer [2] 2-6 6-3 6-4

WINNERS/UNFORCED ERRORS
Goffin –  20/27
Federer – 28/37

ACES/DOUBLE FAULTS
Goffin –  7/1
Federer – 7/3

BREAK POINTS WON
Goffin –  2/3
Federer – 2/11

FIRST SERVE PERCENTAGE
Goffin –  59
Federer – 61

PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Goffin –  73/58
Federer – 74/57

TOTAL POINTS
Goffin –  87
Federer – 83