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.

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.