Carlos Alcaraz comfortably reached the Australian Open fourth round for the first time after opponent Shang Juncheng of China retired with injury.
The Spanish second seed led 6-1 6-1 1-0 when his 18-year-old opponent, who had taken a medical timeout for treatment on his right thigh, ended the match.
It was the first time 20-year-old Alcaraz had played an opponent younger than him at tour level.
"It is not the way anybody wants to move on," Alcaraz said.
Wimbledon champion Alcaraz has now reached the fourth round of all four majors.
He missed last year's Australian Open with a leg injury but is one of the favourites this year to challenge Novak Djokovic for the title.
"I missed the tournament last year," he said. "I was watching the matches at home from the couch, wishing to play in the second week here. It feels special."
His encounter with Shang on Rod Laver Arena lasted just 66 minutes, with the Chinese player visibly hampered in his movement.
Alcaraz will face Miomir Kecmanovic for a place in the quarter-finals after the Serb saved two match points to beat 14th seed Tommy Paul 6-4 3-6 2-6 7-6 (9-7) 6-0.
Elsewhere on Saturday, world number 69 Nuno Borges eliminated 13th seed Grigor Dimitrov to reach the fourth round.
The 26-year-old from Portugal, who has never gone beyond the second round of a Grand Slam before, fell flat on his back as he celebrated a 6-7 (3-7) 6-4 6-2 7-6 (8-6) win over the Bulgarian.
Dimitrov, who came into the Australian Open after winning the Brisbane International, had the chance to force a deciding set at 6-5 in the tie-break but he double faulted and allowed Borges to wrap up the win.
"It's big for Portugal, I guess," Borges said. "I'm proud to be Portuguese and being here and competing in the biggest tournaments in the world.
"I hope I'm showing the younger kids that it is possible. A little bit of luck and working hard, it is possible to achieve. Just living in the moment."
Borges will face Daniil Medvedev, who progressed with a 6-3 6-4 6-3 win over Canada's Felix Auger-Aliassime in just over two hours.
It was a more convincing victory for the Russian third seed compared to his second-round triumph over Emil Ruusuvuori which lasted four hours and finished at 03:40 local time on Friday.
"It was not easy, I'm not feeling fresh, I'm not feeling 100%," Medvedev said.
"At least I have this super ability that I can sleep where I want, whenever I want. When I was younger, I would go out at night after matches and sometimes train without sleep. Maybe that helped me play today."
The 2021 US Open winner said he is feeling more "at peace" with himself recently.
"Honestly, I felt like I was always a happy person in life. I think now even more," he said.
"I feel like I know where I'm going. I know what I have to do in life."
German sixth seed Alexander Zverev beat Alex Michelsen 6-2 7-6 (7-4) 6-2 to set up a last-16 meeting with British number one Cameron Norrie, who defeated Casper Ruud in four sets.
French wildcard Arthur Cazaux, the world number 122 who knocked out eighth seed Holger Rune in the second round on Thursday, has also eliminated Dutch 30th seed Tallon Griekspoor with a dominant 6-3 6-3 6-1 victory.
Cazaux, 21, will take on Pole Hubert Hurkacz after the ninth seed came from a set down to win 3-6 6-1 7-6 (7-4) 6-3 against France's Ugo Humbert.
BBC