Millman was just two points away from sealing his reputation as living, breathing Federer-kryptonite when he lead 8-4 in the mind-blowing fifth set tiebreak.
Having shocked the world to upset Federer at the 2018 US Open, Millman nearly made lightning strike twice before the 20-time grand slam champion produced a miracle, peeling off the last six points to steal the tiebreak 10-8.
He did it with the sheer, dumb luck of guessing correctly on match point when Millman approached a soft mid-court groundstroke with a looping forehand that he could have come into the net on.
Instead of an expected clean winner down the line, he had to watch on as Federer predicted the direction of Millman's approach shot and sent back a whipping cross-court, passing shot winner.
Just like that, it was over.
Only a cruel person would say Millman lost it.
"I'll cop it on that one," he said.
"My friends and family and support team, they'll have my back on that one.
"It still hurts to be honest with you. I would have rather lost 10-5 or something.
"Obviously it would have been great to have served an ace and have a few matches and put it to bed but it didn't happen.
"You know, s***, I played some all right tennis to get to that stage."
As well as his commanding tiebreak lead the Queenslander broke the world No. 3 early in the fifth set but wasn't able to consolidate on his own serve. He had another opportunity to break the Swiss great at 3-3, with two break points but that window snapped shut.
His heartbreak was just one of several sources of ridiculous drama that had the tennis world transfixed on their contest.
In the end it was Aussie tennis great Dylan Alcott that explained the raw drama the best.
"It is unbelievable down here,' he told Channel 9 from his courtside position inside Rod Laver Arena.
"It is like every single person in Rod Laver Arena is 100 per cent going for both players. They are riding every single point.
"Oh, we have got an absolute treat out here tonight. Unbelievable."
It was also unbelievable punishment for the two combatants.
Federer revealed after the match it took him to a dark place.
"The demons are always there, they were lurking," he said.
"John deserves more than half of this one."
Aussie tennis great Todd Woodbridge said it would have been even tougher for Millman after being so close that he could taste victory.
"It will be devastation for John Millman," he said.
"He played such an epic match. Standing ovation for him as he leaves the stadium.
"Roger Federer was pushed to the limit."
FEDERER COMPLETELY GONE AFTER EPIC
An exhausted Roger Federer has admitted he would have lost against John Millman had their five-set thriller not been played under the new super tiebreak rules introduced for the first time at the Aussie Open this year.
Federer had lost his three most recent five-set grand slam matches before overcoming Millman in the breaker.
Federer said super fit Millman would have eventually broken him had the match continued to be played until one of them secured a two game lead after 6-6 in the fifth.
"Oh, God. It was tough. Thank God it is a super tie-breaker otherwise I would have lost this one," he said.
"Where do I start? I think John played a great match. He might as well have been a hero in the match. Can't even speak any more. It was a great fight... it came down to the wire at the end."
Federer next meets Hungarian Marton Fucsovics with world No.12 Fabio Fognini the only other seed left in their depleted quarter of the draw.
WORLD REACTS TO MODERN DAY EPIC
On a wild day of upsets and drama that will live long in the memory of tennis fans, the biggest shock of all was very nearly saved for last.
Federer's miracle escape against Millman came after Serena Williams was bundled out by world No. 29 Wang Qiang, while a host of top ten seeds in both the mens and women's draws were also knocked out.
The day of drama has been described by some tennis commentators as "absolutely bonkers".
Had Federer fallen, it would have been the first time since the 1999 French Open that he and Serena would have been eliminated on the same day in the first week of a grand slam. They were both 17-years-old at Roland Garros 21 years ago.
