David Goffin is through to face Roger Federer in the last four of the ATP Finals after defeating Dominic Thiem 6-4, 6-1 on Friday.
From 0-3, 0-15 down in the opening set, the No. 7-ranked Goffin won 15 consecutive points to take control of the match, and never looked back.
Goffin will face six-time champion Federer at the O2 Arena on Saturday. Grigor Dimitrov and Jack Sock meet in the other semifinal.
Having already secured qualification with wins over Thiem and Goffin, Dimitrov later plays his final round-robin match against Pablo Carreno Busta.
Goffin, who was coming off the back of a 74-minute thrashing by Dimitrov, was this time able to recover from another slow start.
Having turned around the first set, he broke Thiem, hampered by a left knee injury, three times in the second to seal a convincing victory.