Stefanos Tsitsipas put friendship aside to crush Mikael Ymer and race into the Australian Open fourth round Saturday, saying that playing in front of empty stands reminded him of when they hit together during quarantine.

The pair were born within weeks of each other and were often pitted together as juniors, but Greek fifth seed Tsitsipas swatted the Swede 6-4, 6-1, 6-1 on John Cain Arena.

He will now play either big-hitting ninth seed Matteo Berrettini or 19th-seeded Russian Karen Khachanov for a place in the last eight as he targets a maiden Grand Slam title.

"It took some time to get used to conditions on John Cain. But I'm very happy with my game. I showed good quality of tennis today," said Tsitsipas.

"Mikael is someone I've known for a long time and it's quite important for me to have battles like this against him, and for the next generation of tennis as well," he added.

"All of have been working very hard to get where we are today."

Tsitsipas said before the match that he had known Ymer "like, since a baby" and the 22-year-olds were quarantine training partners when they arrived in Australia for the year's opening Grand Slam.

He said playing without spectators, after Melbourne went into a five-day coronavirus lockdown, reminded him of their hitting sessions in quarantine.

"I was practising with Mikael during our quarantine we had to undergo for 14 days, so it kind of reminded me of the same conditions as the quarantine. It wasn't much different," he said.

"The crowd, I don't know if the crowd would make it any different. My game was there, and that's the most important thing for me."

Despite their affinity, they had only played each other once before at Tour level, with Tsitsipas claiming a 6-1, 6-3 victory last year in Marseille.

Ymer, ranked 95, stunned last month's Delray Beach titlist Hubert Hurkacz in the opening round then overcame 17-year-old Spanish wunderkind Carlos Alcaraz, but he was no match for the Greek.

Tsitsipas, a semi-finalist at Melbourne Park in 2019, was coming off a gruelling five-set win over Australian Thanasi Kokkinakis, but showed few signs of tiredness.

He took his chances when presented in the opening set then romped through the second, powering down big serves and hitting 10 winners.

The third set followed a similar pattern with Ymer unable to deal with the Greek star's unrelenting accuracy on service return, hitting too many unforced errors and unable to get into the rallies.