MELBOURNE, Australia (AFP) — Ten-time champion Novak Djokovic reached the Australian Open quarterfinals without striking a ball Sunday after his Last-16 opponent Jakub Mensik withdrew.

The pair were due to play in a night match on center court on Monday, but "super sad" Czech star Mensik pulled out with an abdominal injury.

His withdrawal means Djokovic will play Italian fifth seed Lorenzo Musetti or American ninth seed Taylor Fritz for a place in the semi-finals.

"Unfortunate decision to make for me," said rising star Mensik, who beat American Ethan Quinn in three sets to set up the Djokovic clash.

"After the last couple of matches I started to feel worse, and actually the problem is my abdominal muscle on the left side.”

"I think if I would step on the court tomorrow, it would be such a big risk for me for my next weeks, for my next tournaments, and actually for my health.”

"The fact that my fourth-round match was to be against Novak on Rod Laver Arena makes it even more difficult," added the 20-year-old. 

"So, of course, I'm super sad not to step on the court and to compete against my idol and the GOAT."

Djokovic became the first player to win 400 Grand Slam matches when he swept past Dutchman Botic van de Zandschulp in three sets to set up the Mensik match.

The 24-time Slam winner is in good form so far as he bids to shatter the recent dominance of Jannik Sinner and Carlos Alcaraz. 

Since his last Slam title, in 2023 at the US Open, Alcaraz or Sinner have shared all eight majors.

Also advancing is Learner Tien, who battled through a nosebleed to thrash three-time finalist Daniil Medvedev to make a Grand Slam quarterfinal for the first time.

The 20-year-old American, who capped a breakout 2025 by winning the ATP Next Gen title, crushed the Russian 6-4, 6-0, 6-3 in just one hour and 42 minutes on Margaret Court Arena.

It put 25th seed Tien into a last-eight clash with third-seeded German Alexander Zverev.

He is the youngest men's singles quarter-finalist at Melbourne Park since Nick Kyrgios in 2015 and the youngest American man to reach the last eight at a Slam since Andy Roddick in 2002 at the US Open. 

"It feels amazing. I mean, so special to do it, especially here," Tien, who won his first career title in Metz in November, said of making his maiden quarterfinal.

"It's always so special for me to come back and play here.”

"Every year since I've been coming here, the crowd support has been amazing. I don't know why, honestly, a crowd like this with this much energy and support, it means the world to me to do it here."

Defeat was a sorry end for former world number one Medvedev, who was also knocked out last year by then-teenage qualifier Tien, in a five-set marathon.

This time the 11th seed Medvedev, who reached three of the last five finals in Melbourne, was a shadow of his former self.

Tien broke immediately to signal his intent, but his momentum was interrupted when he needed treatment for a nosebleed.

They resumed after a seven-minute break, with Tien taking the set.

After that it was all the American, who reeled off 10 straight games as Medvedev imploded, cutting a dejected figure.

He suddenly woke up and against the run of play won three games to give himself a glimmer of hope, before Tien seized back control and sprinted to the finish.