Roger Federer survived another uncomfortable evening to reach the quarter-finals of the Australian Open.

Having been pushed to the brink by John Millman in a late-night classic on Friday, Federer again dropped the opening set to Hungary's Marton Fucsovics.

But this time he did not need a deciding set, scrapping hard in cool, breezy conditions to win 4-6 6-1 6-2 6-2 after two hours and 11 minutes.

"I'm going to have to serve well, clearly, and then I think I'm going to have to get my return at a high percentage, make him play a lot of those points, and then try to be efficient on my service games," said Raonic.

Federer's next opponent is American Tennys Sandgren, who is once again playing well above his ranking at a slam.

Ranked 100, Sandgren is through to the quarter-finals here for the second time in three years after winning a wild contest against 12th seed Fabio Fognini 7-6 (5) 7-5 6-7 (2) 6-4.

Sandgren's politics were the focus two years ago but here he was something of a sideshow to the volatile Fognini, who rowed with the umpire and the supervisor, took a long bathroom break and received a point penalty.

Sandgren implied in an on-court discussion that he believed Fognini was allowed to bend the rules, and he explained later: "It seemed odd that we probably were already at time between the first and second set, then there was a bathroom break.

"I would have liked to have seen the ref be a little more forceful for what the times actually were.

"It's a roller coaster sometimes with him. Sometimes you're just a passenger with what's going on.

"He doesn't play well, all of a sudden he's playing amazing, you're stuck with your hands in your pockets like, 'Shoot, I'd like to play tennis, too'."