It was a day of upsets at the Gstaad Open as the top four seeds, Alexander Bublik, Casper Ruud, Valentin Vacherot and Arthur Rinderknech, were all knocked out on Friday.

Top seed Bublik's round-of-16 clash with Quentin Halys was interrupted by rain on Thursday, and the Frenchman got the better of his opponent when play resumed.

Halys returned to the court serving at 5-6 in the deciding set and held firm to claim his 6-7 (4-7) 6-4 7-6 (7-5) victory on his second match point against the reigning champion.

And after Bublik fell, the other big names followed.

Casper Ruud also took the first set of his match, but Juan Manuel Cerundolo earned a hard-fought victory to make it through to the semi-finals.

The Argentinian triumphed 3-6 7-5 6-2, despite trailing 4-2 at one stage of the second set, and completed a stunning turnaround against the second seed in two hours and 15 minutes on the court.

Cerundolo will now face Raphael Collingnon in the final four after the Belgian sank Vacherot in three sets.

Collingnon held his nerve in the first-set tie-break and did not let his head drop after losing the second set, claiming a 7-6 (9-7) 4-6 7-5 win.

And Stefanos Tsitsipas completed the spectacular day on the clay courts, as he reached his first semi-final since winning in Dubai last year as he knocked out fourth seed Rinderknech.

The Greek upset Rinderknech 6-3 3-6 6-3 in one hour and 41 minutes, and will face Aleksandr Shevchenko – who beat Halys in the last eight – for a place in the final.

Top seeds fall like dominoes

Though Halys failed to make it through to the semi-finals, he enjoyed a strong finish to his interrupted second-round match.

He won 92% (46/50) of points behind his first serve and forced seven break points, though he could only convert one of those in a tight contest.

As for Cerundolo, he remains the only player to have defeated Ruud in Gstaad, having also beaten the Norwegian – a two-time champion in 2021 and 2022 – in the 2025 quarter-finals.

The pair saved four break points apiece, with Cerundolo facing six to Ruud's eight, and the Argentinian was thrilled he could take the opportunities presented to him.

"I put all my energy into trying to feel my best," Cerundolo said in his on-court interview. "He was beating me well.

"He was doing better and a break up with the wind in his favour. He made maybe two mistakes so that I could come back in the second set. The break point was unbelievable… Then I managed to win the game, and I started playing really well."