Fourth seed Daniil Medvedev was in cruise control against Alexei Popyrin. AFP/VNA Photo

MELBOURNE — World No 4 Daniil Medvedev eased past Alexei Popyrin in straight sets on Saturday to set up a last-16 clash with former Australian Open champion Stan Wawrinka.

The tall Russian had few problems dispatching the unseeded Australian 6-4, 6-3, 6-2 on Rod Laver Arena as he steps up his quest for a maiden Grand Slam crown.

"I knew it was not going to be easy and happy to win in straight sets," said Medvedev, insisting he had no expectations in Melbourne.

"(But) of course every time no matter what tournament I'm super disappointed (if I lose).

"Hopefully I can win seven matches here, but very tough."

He now plays experienced 2014 champion Wawrinka after the Swiss got an easy ride through his clash against John Isner, with the American retiring injured while losing 6-4, 6-1.

Wawrinka, a former world number three who has never returned to his best since knee surgery in 2017, said he was happy to be in the second week of a Slam once again.

"I think I was playing well again today," he said. "I was really happy the way I was moving, the way I was playing. 

"That's very positive. It's great to be back in the second week, that's for sure. Feeling way better."

Popyrin conceded an early break and was never allowed into the match by a man seeded behind only the Big Three of Rafael Nadal, Novak Djokovic and Roger Federer.

After Medvedev rattled through the first set, Popyrin went off for treatment for a leg problem midway through the second.

When he returned the Russian was ruthless, wrapping up the set then completing a routine victory, using his strength and big serve to good effect. AFP