In a rematch of their classic 2018 US Open fourth-round encounter - won in a huge upset by Millman - the contrasts couldn't be starker.

No titles versus 103. $5 million in prize money v $130 million. No.47 v No.3.

But there's plenty of mutual respect, the Swiss hand-picking Millman to train with him in June 2018 at his Swiss base because of the Queenslander's incredible work ethic; Millman holding Federer in the highest esteem because, well, he's Federer.

As Millman puts it, for lightning to strike twice he'll have to turn Friday's clash into another sweat-soaked battle of attrition, much like his four-set triumph at Flushing Meadows.

"For me, I try to make things as physical as possible. I've got to try to do that. That's how I play," Millman said.

"I've got to try to keep as good a quality as possible because we know that Roger transitions so well, he jumps on anything short. He's so good at moving in and out of the court really quickly. I'm going to have to keep really good quality of shot.

"Hopefully it's slightly heavy conditions. I prefer the slightly heavier conditions like you have up in Brisbane. Probably not too dissimilar to New York, when you get those humid nights, and you feel as if you can really crush the ball and they'll drop in. I'm big on those types of conditions."

Often lost in the glory of their US slug-fest is the fact that the pair have met another two times.

While those matches favoured Federer, they were close-run contests, Millman up a set and a break in Brisbane back in 2015 while also pushing the 38-year-old to a tiebreak on grass in Halle last year.

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

And Millman will need to do that on Friday to be in with a shot at squaring their career ledger at 2-2.

With cooler temperatures likely to mean faster conditions and Federer appearing in red-hot form, the odds are firmly against Millman but the 30 year-old won't die wondering.

"Regardless of the score at the end of the day, I'll go out there and leave it all out there. If lightning strikes twice, I wouldn't say no to it," he said.

The winner is guaranteed an unseeded fourth-round opponent - either American Tommy Paul or Hungary's Marton Fucsovics on Sunday.

Australian Associated Press