Stefanos Tsitsipas produced an excellent performance to beat reigning champion Alexander Zverev and book his place in the ATP Finals last four.
The Greek snared a break late in the first set and never looked back, taking the lead inside the first 38 minutes.
An early break on Zverev's first service proved pivotal in the second as he sealed a 6-3, 6-2 victory in an hour and 13 minutes on court.
The result means Tsitsipas will join Dominic Thiem in the semi-finals, with Zverev failing to grab the one set he needed to delay the 21-year-old securing his passage through.
After a close opening to the contest, Zverev was showcasing his frightening pace on his serve with an 143mph ace. But Tsitsipas was clearly the better operator when moving about the court and when Zverev's serve began to falter, he stepped in to snatch a break at the fourth time of asking in the eighth game.
Cheered on by a large section of fans from his homeland, Tsitsipas never looked in doubt of going on to take the set.
Zverev struggled to find the level of performance he had shown against Rafael Nadal and his frustration started to get the better of him when Tsitsipas broke in the first game.
The youngster looked unbeatable in this form and when he took a double break in the fifth game, it clear there was only man winning this. Zverev soon found himself 5-1 down and facing an impossible task, there was no Nadal-esque comeback in sight.
Sure enough, Tsitsipas made certain of the win with a comfortable hold over the resigned Zverev and he had done it. It means there will now be a straight shootout between Nadal and Zverev in their final group matches on Friday for the last qualifying spot from Group Andre Agassi.
