David Goffin stunned six-time champion and world no 2, Roger Federer by coming from a set down to win and progress to the ATP finals.
The Belgian who also defeated world no 1, Rafael Nadal a few days ago, recorded his first win 2-6 6-3 6-4 in seven attempts against the 19-time Grand Slam champion.
The other semi-final of the day, saw sixth seed, Grigor Dimitrov defeat Jack Sock after falling behind in the first set.
Dimitrov however came back to win 4-6 6-0 6-3 against the American and progress to the finals where he will play David Goffin.
Dimitrov and Goffin will meet for the second time this week, with the Bulgarian defeating the Belgian 6-0 6-2 in the group stage on Wednesday.