Stefanos Tsitsipas was in dreamland after dethroning Roger Federer and Frances Tiafoe said his phone was "blowing up" after reaching the Australian Open quarter-finals on his 21st birthday.

Tsitsipas struck a huge blow for the next generation by consigning Federer to a first defeat at Melbourne Park since 2016, winning a fourth-round thriller 6-7 (11-13) 7-6 (7-3) 7-5 7-6 (7-5).

Tiafoe also demonstrated the exuberance of youth to topple 20th seed Grigor Dimitrov 7-5 7-6 (8-6) 6-7 (1-7) 7-5 and reach the last eight of a major for the first time.

The unseeded American will face Rafael Nadal, who ousted Tomas Berdych in straight sets.

Marathon man Roberto Bautista Agut also broke new ground at a grand slam at the age of 30, reward for winning a third five-set contest of the opening week as last year's losing finalist Marin Cilic bowed out.

STEELY TSITSIPAS UNBREAKABLE

Federer looked to be heading through when he applied huge pressure on an opponent 17 years his junior in the second set after winning the first.

Tsitsipas fended off four break points in long back-to-back service holds and stood firm to save another four in a gruelling 10th game.

The steely 14th seed took the first set off Federer in the tournament by winning a second tie-break and claimed the only break point of a tight match to move a set away from securing the biggest win of his career.

Tsitsipas saved all 12 break points he faced, coming out on top in a third breaker to end Federer's 17-match winning run in the first major of the year - having also avoided being broken by the Swiss master in a Hopman Cup defeat this month.

TIAFOE SILENCES DIMITROV

Tiafoe has made a name for himself in the first week of the tournament and he will compete in the second week of a grand slam for the first time after seeing off Dimitrov.

The world number 39 treated the Melbourne Arena to his LeBron James-style 'Silencer' celebration after marking his birthday in style and revealed his phone has been red hot.

"My phone is blowing up. I can barely use it. It's just what you dream about. I told my coach, Zack Evenden, my agent, Alex, 2019 I'm going to pop off. No reason why I can't do these things," Tiafoe said.

"I didn't think it was going to happen right away. This is unbelievable, man."

DURABLE BAUTISTA AGUT GOES THE DISTANCE AGAIN, NADAL IN CRUISE CONTROL

Bautista Agut has certainly earned his first grand slam quarter-final appearance, coming through yet another match that went the distance.

The Spaniard beat Andy Murray in a first-round five-setter and John Millman also came from two sets down to force a decider.

Bautista Agut had no such trouble as he got past Karen Khachanov in straight sets, but he needed three hours and 58 minutes to win 6-7 (6-8) 6-3 6-2 4-6 6-4 against Cilic.

Nadal, on the other hand, has not dropped a set in his first four matches following a 6-0 6-1 7-6 (7-4) victory over Berdych.