Australian Alex de Minaur has failed to capitalise on a dazzling start, slumping to a three-set loss to Andrey Rublev in the quarter-finals of the Paris Masters tennis tournament.
The 13th-seeded Aussie claimed the first set against his Russian opponent but couldn't maintain the momentum, with Rublev rallying to win 4-6 6-3 6-1.
De Minaur had progressed to the quarter-finals when he received a walkover after Italy's Jannik Sinner withdrew from the tournament in a scheduling protest.
Earlier, world No.1 Novak Djokovic stayed on course for a seventh Paris Masters title with a gripping 7-5 6-7 (7-3) 6-4 victory over Denmark's Holger Rune.
Despite the defeat, the Dane still qualified for the ATP Tour Finals in Turin.
Djokovic was rock-solid as he avenged his defeat by the tenacious youngster in last year's showpiece to set up a semi-final against fifth-seeded Rublev.
Victory for 20-year-old Rune would have well and truly sealed his place in Turin, but he will still make his debut in the year-ender featuring the world's top eight players because de Minaur had to win the title to deny the Dane a place at the elite event.
Djokovic's victory also means Germany's Alexander Zverev qualifies for the ATP Tour Finals.
Rune delighted the Paris crowd with some stunning tennis and saved a match point at 4-5 in the second set, before an inspired tiebreak took the match to a decider.
But Djokovic was unfazed and broke serve early in the third set, while Rune was not helped by a cut to his hand that required some lengthy patching up at a changeover.
The sixth seed could make no impression on the Djokovic serve in the decider as the top-ranked Serb clocked up a 16th successive win since losing in the Wimbledon final.
"It was quite a similar match to last year's final, it was anybody's game in every set," Djokovic said.
"I played an awful tiebreak in the second set, probably the worst one this year.
"But again credit to him for staying mentally tough and playing solid. We have similar games - move well, defend well and all-round players."
Grigor Dimitrov booked his spot in the semi-finals with a 6-1 4-6 6-4 win over Poland's Hubert Hurkacz that ended his rival's hopes of qualifying for the ATP Finals.
Despite hitting 19 aces, Hurkacz dropped his serve three times, with his defeat meaning he can no longer finish among the top eight players who will make it to the end-of-season showpiece in Turin.
The 32-year-old Dimitrov is in the last four at the indoor tournament for the second time.
The rejuvenated Bulgarian will now meet Greek star Stefanos Tsitsipas, who looked his best when he outplayed former Paris winner Karen Khachanov 6-3 6-4 for his 300th career win.
Dimitrov has been enjoying a good run of form, also reaching the semi-finals at the Shanghai Masters last month.
"My body is feeling well for now, that's the most important thing," said Dimitrov, who converted all three break points he had.
"My head is good. If I'm able to play like that on a consistent basis throughout every game, I put myself in a position to do better. Today was no different."