Spain's Carlos Alcaraz serves against China's Shang Juncheng during their men's singles match on day seven of the Australian Open tennis tournament in Melbourne on Jan 20, 2024. (PHOTO / AFP)

MELBOURNE - Carlos Alcaraz eased into the fourth round of the Australian Open for the first time on Saturday after Chinese wildcard Shang Juncheng retired hurt while trailing their uneven contest 6-1 6-1 1-0.

In the unusual position of playing someone younger than himself, twice Grand Slam champion Alcaraz had simply dominated 18-year-old Shang for just over an hour on Rod Laver Arena.

Shang, known as "Jerry" at his Florida training base, had taken a medical timeout for treatment on his thigh at 4-1 down in the second set and gave up the ghost after being broken for the sixth time at the start of the third.

China's Shang Juncheng serves against Spain's Carlos Alcaraz during their men's singles match on day seven of the Australian Open tennis tournament in Melbourne on Jan 20, 2024. (PHOTO / AFP)

"It's not the way anybody wants to move on and I wish him a speedy recovery," said second seed Alcaraz, who will play Serbian Miomir Kecmanovic in the last 16.

"He started the year unbelievable, playing great games, and I was looking forward to playing this match ... I think Jerry and myself wanted to play a long match."

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Shang broke new ground for China when he reached the second round as a qualifier last year and was looking to become the first Chinese man to reach the last 16 of a Grand Slam since 1938.

The teenager was unable to muster sufficient power on his serve to be confident of holding, however, and did not have enough game on returns to get a look at the Spaniard's.

Carlos Alcaraz (left) of Spain is congratulated by Shang Juncheng of China following their third round match at the Australian Open tennis championships at Melbourne Park, Melbourne, Australia, on Jan 20, 2024. (PHOTO / AP)

Alcaraz barely needed to move out of first gear as he eased through the first two sets, throwing in the occasional stunning lob or crosscourt winner to keep the crowd engaged.

Last year, the 20-year-old watched the year's first Grand Slam from his couch nursing a hamstring injury and he was delighted to get through to the business end of the tournament for the first time in three visits to Melbourne Park.

"This is the first time I've played the second week here and it feels special," he added.

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"Coming to this tournament this year, I was looking to improve the result that I did in 2022. I did it. And now is the time to keep going, play better and better, and hopefully go through more rounds."