Stefanos Tsitsipas won a battle of quarantine practice partners on Saturday, defeating longtime friend Mikael Ymer 6-4, 6-1, 6-1 to reach the fourth round of the Australian Open.

The fifth seed needed four hours and 32 minutes to survive home favourite Thanasi Kokkinakis’ upset bid in the second round. But Tsitsipas had no such trouble against his Swedish foe on John Cain Arena, reaching the Round of 16 after one hour and 34 minutes.

“I think I kept things simple [and] didn’t complicate whatever tactics or whatever use of my game I wanted to execute today,” said Tsitsipas. “I’d say I entered a little bit stressed in the match. I don’t know why, for which reasons, but over time I got used to the conditions, to the big court, and I think I managed to sustain my level and even raise my level once I got a few breaks ahead. That gave me a lot of confidence, and I felt like I was on top of my game at that point.”

The match was tight early on, as Ymer showed the talent that helped him to a spot in the 2019 Next Gen ATP Finals. But the World No. 95 played a loose service game at 4-5 in the first set, getting broken at love to drop the opener. From there, the momentum firmly moved in Tsitsipas’ direction.

The 2019 Nitto ATP Finals champion played a clean match, making just 20 unforced errors in his victory compared to 36 for Ymer. The Swede went for more as the match went on, but it rarely made an impact on the Greek star, who welcomed the unforced errors sent to his side of the court.

Tsitsipas, who reached his maiden Grand Slam semi-final at this event in 2019, will next play ninth seed Matteo Berrettini. The Italian found his best tennis in crucial moments to overcome Karen Khachanov 7-6(1), 7-6(5), 7-6(5).