Federer was unstoppable in his round two match against Serbian Filip Krajinovic, taking just over an hour and a half to nail a 6-1 6-4 6-1 victory.

The third seed barely put a foot wrong with the Rod Laver crowd with commentators also in raptures after a performance that included 42 winners.

But attention quickly turned to Federer's match-up with Millman, who also had a straight sets second round win over Poland's Hubert Hurkacz.

The Australian famously ousted the 20-time major champion in the the round of 16 at the 2018 US Open, winning in four sets 3-6 7-5 7-6 (9-7) 7-6 (7-3).

The result is one Federer hasn't forgotten.

"I almost passed out when I played out against him in New York," the 38-year-old said.

"It was so hot but he had no problem as he's from Queensland, so he was like normal stuff."

The pair have met a two other times while Federer has got the result, they have always been tight affairs.

Federer said he had practised a lot with world No.47 Millman and rated him as one of the fittest players on the tour.

"He's a super good guy and an unbelievably tough opponent," he said.

"There's not many guys fitter than him out there and those are the guys I respect the most, actually, because he gets the most out of the game."

Australian Associated Press