Stefanos Tsitsipas shocked six-time champion Roger Federer 6-3, 6-4 to reach the final of the ATP Finals in his tournament debut on Saturday.
The Greek sixth seed, 17 years younger than his opponent, beat the Swiss at the Australian Open but had fallen to him twice since then.
Federer was unrecognisable from the player who dominated Novak Djokovic in his final round-robin match, struggling on serve and hitting a total of 26 unforced errors compared with just five against the Serbian.
But Tsitsipas belied his years with a performance full of confidence and grit, saving 11 out of 12 break points during the match.
Great performance
“I'm so proud of myself today, a great performance and once again the people were great,” he said.
Earlier on Friday, Rafael Nadal headed home after defending champion Alexander Zverev's win against Daniil Medvedev confirmed the Spaniard's exit from the season-ending tournament.
Zverev’s 6-4, 7-6(4) win meant he qualified for the semifinals from Group Andre Agassi.
The results: Semifinal: Stefanos Tsitsipas bt Roger Federer 6-3, 6-4.
Group Andre Agassi: Alexander Zverev bt Daniil Medvedev 6-4, 7-6(4) .
