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.”