Former world No 1 Daniil Medvedev crashed out of the Dubai Championships on Thursday, squandering four match points before losing a bad-tempered quarterfinal to Tallon Griekspoor of the Netherlands.
The 47th-ranked Dutchman came through 2-6, 7-6 (9/7), 7-5 as the world No 6 imploded.
Medvedev, the 2023 champion in Dubai, was handed a code violation for unsportsmanlike behaviour after seeing match points slip away in the second set.
As his frustration boiled over, he accused umpire Adel Nour of applying "double standards" with Russian players.
Nour hit back, telling Medvedev that he treats all players in the same way, regardless of nationality before brushing away the top seed's complaints.
Griekspoor kept his cool in the deciding set, taking victory on a fourth match point of his own.
Medvedev refused to shake hands with Nour at the end of the tie.
The 28-year-old Griekspoor, who saved three match points to see off Roman Safiullin in the first round and then overcame defending champion Ugo Humbert, will face Stefanos Tsitsipas for a place in the final.
Fourth seed Tsitsipas battled to a 7-6 (7/5), 1-6, 6-4 win over Italy's Matteo Berrettini to reach his first semifinal since July last year.
"I'm super happy with this win," said Griekspoor.
"Daniil is an unbelievable player, an unbelievable competitor. He's been at the top of the rankings for so many years, so I'm very pleased with this win.
"I was a little bit lucky on the match points down, and in the second-set tie-break. I even needed a few match points myself to finish this one off."
Canada's Felix Auger-Aliassime notched up a Tour-leading 15th win of the year, seeing off former US Open champion Marin Cilic 6-4, 3-6, 6-2 to reach his fourth semifinal of 2025.
"It's been a great start," said 21st-ranked Auger-Aliassime who has already claimed titles at Adelaide and Montpellier this year.
Auger-Aliassime will face French qualifier Quentin Halys who came back from a set and break down to defeat Italian lucky loser Luca Nardi 2-6, 6-3, 7-6 (7/5).
Halys knocked out ninth-ranked former champion Andrey Rublev in the first round.