Stefanos Tsitsipas made light work of defending ATP Finals champion Alexander Zverev to book his place in the last four in London with a 6-3 6-2 victory.
Zverev outdid world number one Rafael Nadal on Monday but could not match the speed, power and precision shown by Tsitsipas, who has made the semi-finals on his first appearance in the season-ending tournament.
A break on Zverev's final serve of the opener put the 21-year-old in control, with another concession of serve from the world number seven following at the start of set two.
With victory firmly in his sights, Tsitsipas did not let up as he charged on to serve out a dominant triumph in just 75 minutes.
"I was really surprised by my performance," Tsitsipas said. "I did everything right. I just played my game. I had a clear picture on the court."
After an even start, it was Tsitsipas who made the breakthrough.
Having played two excellent drop shots in succession to hold serve, the Greek broke with an exquisite return onto Zverev's toes to lead 5-3.
Tsitsipas took the 39-minute set at the first time of asking – Zverev sending a lob just beyond the baseline.
The German survived two break points at the start of set two, with a fine backhand pass at the culmination of a long rally forcing deuce.
But Tsitsipas could smell blood and, after squandering another chance to break, did so at the fourth time of asking with a combination of superb backhand efforts.
Tsitsipas failed to take another break point at 3-1 up, sending a makeable passing stroke out of play, but made no mistake at the next time of asking with a perfectly constructed attack.
Zverev challenged well to stay in the match, but it merely stalled the inevitable as Tsitsipas – who faces Nadal in his final group match – went on to secure a fourth straight win over his opponent with a sweetly struck ace.