In a match pitting the oldest and youngest players left in the men’s draw, the 20-year-old Tsitsipas overhauled Federer 6-7(11) 7-6(3) 7-5 7-6(5) under the lights of Rod Laver Arena, sparking delirium among Greek fans out in force at Melbourne Park.
The 37-year-old Federer, 20 times a Grand Slam champion, will rue his chances, having failed to convert any of the 12 break points he took from Tsitsipas over the course of a riveting clash laden with sparkling shot-making.
Instead, it was Tsitsipas showing a wise head on young shoulders in a final tiebreak of unrelenting tension.
When given a match point after Federer slapped a forehand long, he converted it clinically, forcing a backhand error from the Swiss to announce himself on one of the game’s biggest stages.
He raised his arms in triumph and roared at the terraces, bringing tears of joy to his brother’s eyes in the players’ box.
“There’s nothing I can describe, I cannot describe it, I am the happiest man on earth right now,” Tsitsipas said in his courtside interview.
“Roger is a legend of our sport, he showed such good tennis over the years. I have been idolising him since I was six.
“I didn’t lose my patience, stayed in those rallies. It was very important to save those breakpoints.”
Tsitsipas may be set for even bigger prizes, with a semi-final on offer should he beat 22nd-seeded Spaniard Roberto Bautista Agut.
When the dust settles, Federer will note that he has been upset in the last 16 at the last two Grand Slams, having fallen to unseeded Australian John Millman at the U.S. Open.
“Definitely didn’t go the way I expected with the breakpoints,” Federer told reporters.
“I have massive regrets tonight. I might not look the part, but I am. I felt like I had to win the second set. Cost me the game tonight.”
Federer saw something of his old self in Tsitsipas, a rangy tyro with flowing, blond locks, and unswerving confidence.
“He has a one-handed backhand and I had long hair, too. So yeah, a little bit,” he remarked.
There was no easing into the intergenerational battle, with Tsitsipas having a first serve canceled for twice falling foul of the clock in the opening game. He had to stave off two break points to hold.
Sparkling winners sang off both racquets as the first set flew into an epic tiebreak of blown chances and brave saves.
Tsitsipas finally relented when he pushed a forehand wide, having been wrongfooted by a deep and venomous shot.
Lesser opponents might have fallen into a funk against the front-running Swiss but Tsitsipas stayed brave under fire.
He saved eight break points in the second set to keep Federer at bay yet had no such gifts on his opponent’s serve.
The Greek stared down four set points when serving at 5-4 and finally held with a net-rush and a volley.
He fired a backhand crosscourt into the net-bound Federer’s sneakers to earn three set points in the tiebreak, then converted the first with a crushing forehand winner that kissed the line in the corner.
Federer became concerned as more break points went begging in the third set, and he was soon clinging desperately on serve.
It came to a head at 6-5 down, with Federer’s first serve going missing in four successive points and the set lost with a trio of unforced errors on forehand.
The Swiss held on until deep into the decider but it seemed time was catching up with him.
Tsitsipas, 17 years his junior, never dropped his guard, and Federer will leave Melbourne Park without a quarter-final appointment for only the second time in 18 years.