Novak Djokovic and Roger Federer both suffered quarter-final exits at the Shanghai Masters on Friday, guaranteeing a first-time winner of the tournament this year.
The top two seeds were widely expected to contest the final but succumbed to Stefanos Tsitsipas and Alexander Zverev respectively.
Daniil Medvedev and Matteo Berrettini also secured their progress to settle the semi-final line-up in China.
And there was an added bonus for Tsitsipas as he claimed a spot at the ATP Finals.
DJOKOVIC DOWNED BY TSITSIPAS' 'BEST COMEBACK'
Tsitsipas recovered from a set down to beat reigning champion Djokovic 3-6 7-5 6-3 and labelled it his "best comeback".
The Greek will now face Medvedev in the last four, having earned an end-of-season Finals spot courtesy of the Russian's 6-3 7-6 (7-4) win over Fabio Fognini.
"It's the best comeback that I have ever had, probably," said Tsitsipas.
"I would say also [the] Federer comeback in the Australian Open wasn't easy. I lost the first set against one of the best tennis players in the world and managed to win three consecutive sets after that.
"Same today, but with less sets, two sets, which was quite difficult for me to pull out. It was a very difficult victory mentally, too.
"I wasn't really thinking that long term that I have to win two sets. It just went step by step. It happened."
FRUSTRATED FEDERER FALLS TO ZVEREV
Federer is usually a picture of calm on the tennis court, but he was evidently ruffled in his 6-3 6-7 (7-9) 6-3 loss to Zverev.
The Swiss, who rescued five match points to win a remarkable second set, was docked a point in the fourth game of the decider after hitting the ball into the crowd in anger.
His frustration may have stemmed from an inability to find his rhythm against an inspired Zverev, who was 40-0 up when serving for the match in the second set.
Having seemingly thrown his chances away, Zverev dug deep and broke Federer at the first opportunity in the final set to claim an advantage he refused to surrender.
Berrettini awaits, the Italian having overcome Dominic Thiem 7-6 (10-8) 6-4.