World number one Carlos Alcaraz retired injured against Holger Rune at the Paris Masters on Friday, sending his fellow 19-year-old through to the semi-finals, while Novak Djokovic and Felix Auger-Aliassime also sealed places in the last four.
Rune outclassed Alcaraz to win the opening set 6-3 and held firm in the second when the top seed raised his game before the Spaniard retired at 3-1 down in the tie-break having received medical treatment for an abdominal strain at 6-5.
"I cannot stretch. I couldn't serve well, I couldn't hit the forehand well said Alcaraz. "I preferred to retire and see it and take care of it."
Alcaraz was hopeful of making a full recovery for his debut at the ATP Finals in Turin, which begin on Nov. 13, despite the quick turnaround.
"I have some tests on how it's going to be before Turin," he added. "But right now I'm focused on trying to get better in the abdominal and trying to be at 100 percent in Turin."
Holder and sixth seed Djokovic made light work of Italian youngster Lorenzo Musetti in a 6-0, 6-3 win and will next meet Stefanos Tsitsipas, who trounced Tommy Paul 6-2, 6-4 later on Friday.
A six-times winner in Paris, Djokovic served Musetti a 24-minute bagel and dropped only eight points in the first set before overcoming a brief wobble in the second, when he went a break down, to ease to victory.
Danish teenager Rune, bidding to reach four finals in a row, advanced to his first ATP Masters 1000 semi-final and earned his third top 10 win in as many days after seeing off Hubert Hurkacz and Andrey Rublev.
He will take on eighth seed Auger-Aliassime in a battle between two of the Tour's most in-form players and a rematch of the Swiss Indoors final in Basel five days ago, which the Canadian won in straight sets.
Auger-Aliassime extended his winning run to 16 matches after racing to a 6-1, 6-4 win over Frances Tiafoe to remain on track for a fourth ATP title in as many weeks, having also won in Florence and Antwerp during his unbeaten run.
The 22-year-old cruised through the first set but Tiafoe dug deep to hold serve and save five match points before Auger-Aliassime sealed a 93-minute victory on his sixth attempt.
"I feel better and better," Auger-Aliassime said. "Of course right now I'm playing well and feeling good, but I see things that I can still do better and still improve on to be able to top the game."
Sakkari, Sabalenka in WTA Finals semis
A relentless Maria Sakkari capped her perfect run through the round robin stage of the WTA Finals with a 6-2, 6-3 win over Ons Jabeur on Friday to reach the semi-finals in Fort Worth, Texas, along with group runner-up Aryna Sabalenka.
Sakkari broke twice for a 5-1 cushion en route to capturing the first set, which meant Tunisian world number two Jabeur had no mathematical chance of advancing even if she had rallied back to victory.
In the second set, with Sakkari and Sabalenka already safely into the knockout stage, the Greek world number five broke early for a 3-1 lead and raced home from there to improve to 3-0 in the stage of the season-ending tournament.
"I'm trusting myself, I'm just fearless on the court and I am enjoying myself here," Sakkari, who has not dropped at set in Fort Worth, said during her on-court interview.
"There is no secret behind how I am playing but I think it was about time just to start playing good again and I am very happy that it's actually happening here."
By winning her group, Sakkari will face either Frenchwoman Caroline Garcia or Russian Daria Kasatkina in the semis while Sabalenka will face world number one Iga Swiatek.
In the day's first match, Belarusian world number seven Sabalenka eliminated Jessica Pegula from the WTA Finals with a 6-3, 7-5 victory to improve to 2-1.
Sabalenka made a blistering start, breaking Pegula to open the match and again for a 5-2 lead. World number three Pegula then fought off four set points to break straight back but Sabalenka broke to love in the next game to wrap up the set.
Pegula fell behind 2-0 in the second but fought back before Sabalenka, at 3-3, delivered a love hold and then came back from 40-15 down for a crushing service break before the top-ranked American returned the favour to extend the set.
But Sabalenka held to love for the third time in the set and fourth in the match for a 6-5 lead and then closed it out on her second match point when she ripped a backhand crosscourt winner.
"She's an amazing player and she made me really work tonight," said Sabalenka.
"Just happy that I was really focused from the beginning to the end and I was able to finish this match in two sets."