Former champion Stan Wawrinka shocked Russian fourth seed Daniil Medvedev in five sets to reach the Australian Open quarter-finals with a 6-2 2-6 4-6 7-6 (7-2) 6-2 victory.

Medvedev came into the contest having won both their career meetings at Grand Slams in four sets, but the 2014 Australian Open champion took the opening set with a double break of the Russian's serve.

Medvedev, who lost to Rafa Nadal in five sets in last year's US Open final, levelled the contest by breaking Wawrinka twice in the second and nosed ahead in the match with a break in the seventh game of the third.

But Wawrinka refused to yield and took the fourth set tiebreaker comfortably before breaking Medvedev twice in the fifth to set up a quarter-final against either German seventh seed Alexander Zverev or 17th seed Andrey Rublev of Russia. 

Fifth seed Dominic Thiem stretched his flawless record against Gael Monfils with a comfortable 6-2 6-4 6-4 victory to reach his maiden quarter-final in Melbourne.

Thiem, twice a French Open finalist, came into the fourth-round clash against the 10th seed having won all five of the matches they have previously played and did not face a single break point against the Frenchman on the Rod Laver Arena.

"I think that I played my best match so far of this Australian Open. A very, very good feeling," the Austrian said.

"The score looks way easier than the match was. I think I was lucky to make an early break in each set and then was managing to hold my serve well. I'm so happy because I'm for the first time in the quarter-finals here."

Thiem, who lost to Rafa Nadal both times in the title match at Roland Garros, converted four of his 14 breakpoint chances and hit 31 winners to seal the contest.

Monfils surprised Thiem with an underarm serve in the second set, which the Austrian was unable to return, but the world number five managed to chase down most of the drop shots that the Frenchman employed against him.

"I always played my best tennis against him, so maybe that's one reason," Thiem said of his 6-0 record against Monfils.

The 26-year-old will meet the winner top seed Nadal for a place in the semi-finals.