Top-seeded Alexander Zverev advanced to an ATP Toronto Masters quarterfinal against defending champion Alexei Popyrin as his fourth-round opponent Francisco Cerundolo was forced to retire with an abdominal injury on Saturday.
Germany's Zverev secured a 6-4, 1-0 victory, Argentina's Cerundolo taking a medical timeout after the fifth game and finally calling a halt after less than an hour on court.
Australia's Popyrin won his ninth straight match in Canada, beating ninth seed Holger Rune 4-6, 6-2, 6-3.
The 26th-ranked Aussie profitted from nearly 40 unforced errors from his Danish opponent, who has been taking occasional advice from Andre Agassi.
With Popyrin on the horizon, Zverev said he was headed back to the practice court after his abbreviated victory, but he paid tribute to Cerundolo first.
"He's an incredible player, we have a close personal relationship," Zverev said of Cerundolo. "I know about abdominal injuries.
"You can't serve or accelerate on the forehand. He had tears in his eyes when he had to quit. He didn't want to disappoint the crowd.
"But they can last from a few days to a few months. I have respect for him - he beat me three times before tonight."
Zverev, the 2017 champion, will be playing his fifth quarterfinal in seven Canadian appearance.
Earlier, Popyrin saved a break point with his sixth ace against Rune as he served for victory in the final game, finishing the job with a lob winner which left Rune flat-footed.
"This win means a lot," the Aussie said. "I started the week not high on confidence but I knew my game was there.
"I just let go of the pressure and it worked out for me," added Popyrin, who said dropping the first set did not sit well.
"I told myself to keep going and managed to play aggressive on the next break point that I got. From then on I felt much more comfortable."
KHACHANOV TOPPLES RUUD
Karen Khachanov reached his second straight prestige quarterfinal, ambushing eighth seed Casper Ruud 6-4, 7-5 to continue his ATP hot streak.
Game, Set, Masterclass 👨🎓@karenkhachanov is a Masters 1000 quarter-finalist for the 10th time in his career! @NBOtoronto | #NBO25 pic.twitter.com/iApsDt0zVh
— ATP Tour (@atptour) August 2, 2025
Khachanov next faces Alex Michelsen, who claimed his first Masters last-eight place with a 6-3, 6-3 victory over fellow American and good friend Learner Tien.
Khachanov was playing his first tournament since reaching the Wimbledon quarterfinals last month.
The world number 16 reeled off 18 straight points on serve over the first and second sets and produced love games in his final two service games of the match.
Khachanov is SO back 🔥
— Tennis TV (@TennisTV) August 2, 2025
Karen scores his first Top 20 win of 2025, beating Ruud 6-4 7-5 to reach his 10th ATP Masters QF!#NBO25 pic.twitter.com/zo0FkLy1NP
Norway's Ruud, playing his second event after skipping Wimbledon because of injury, was never able to gain control, although he rallied from 4-2 down in the second set to level at 4-4 before Khachanov got back on track.
"I had nothing to complain about until this point," Khachanov said. "I tried to control play and my game plan was working, especially with the first serves.
"It became difficult, but I'm super-glad I was able to put everything together at the end and finish the match."
Michelsen took full advantage of 42 unforced errors from Tien to close out their match in 81 minutes.
"It feels really good," the 20-year-old winner said. "It's uncharted territory from now on. I'm super-happy to be in the quarters."
Michelsen said that despite the raft of errors from Tien he had to take care with his own forehand to claim the victory.
"I hit my forehand super-well today and I knew that if I didn't I would be in trouble," he said.