David Goffin has stunned stun six-time champion Roger Federer to 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 at 20:00 GMT.
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 at 18:00.
Federer, 36, had been a strong favourite to land his seventh title at the season finale, but will be absent from Sunday’s final after suffering only his fifth defeat of 2017.
The Swiss can reflect on a remarkable year in which he has won two more major titles, among 52 match victories, but it is six years since he last won the ATP Finals.
“It’s a bit disappointing for me because it’s indoors, it’s a court I like to play on, but I had my chances and missed them,” said Federer.
“When he had them, he was very committed. I think that was the difference.
“He’s crushed me too many times in practice to not also do it once in a match situation.”