London : David Goffin mounted a spirited fightback to stun six-time champion Roger Federer and reach the final of the season-ending ATP Finals in London.
The Belgian seventh seed, 26, came from a set down to win 2-6 6-3 6-4, his first victory in seven attempts against the 19-time Grand Slam champion.
“I have no words. I cannot describe how I’m feeling - so much joy, so much happiness,” said Goffin.
Grigor Dimitrov will face Jack Sock in the second semi-final.
Britain’s Jamie Murray and Brazilian Bruno Soares take on defending champions Henri Kontinen and John Peers in the doubles semi-finals at the O2 Arena.
Federer, 36, went into the semi-final with a 6-0 record against Goffin, whose resistance appeared to have been broken after only seven minutes.
Goffin battled gamely to cling on in his opening service game but Federer took it on the fifth break point and went on to dominate the set. Two rasping backhand winners down the line helped the Swiss to a second break at 4-1 and the set was wrapped up in little over half an hour.
The match turned early in the second set, when Goffin swung a cross-court forehand into space vacated by Federer to edge 2-0 ahead. What at first appeared to be an exercise in damage limitation grew into an increasingly potent threat as Goffin’s serve subdued Federer, who fired a forehand long on his only break point in the set.
When Goffin broke in game three of the decider, helped by a beautiful backhand up the line, his belief spread to the 17,000 spectators, thrilled by this unexpectedly tight contest.
A surprisingly flat Federer could not muster another challenge as Goffin served out in style to reach the biggest final of his career and guarantee a new champion on today night.