Defending champion Roger Federer was stunned by fiery Greek Stefanos Tsitsipas who ended his bid for a record seventh Australian Open Sunday as a rampant Rafael Nadal continued to scatter rivals.

The Swiss master caved in under the energy and pressure of a man 17 years his junior to tumble out 6-7 (11/13), 7-6 (7/3), 7-5, 7-6 (7/5) in the last 16 on Rod Laver Arena. The man Federer beat in last year’s final, sixth seed Marin Cilic, was also sent packing by Spain’s Roberto Bautista Agut, who now plays Tsitsipas in the quarter-finals.

Five-time Grand Slam winner Maria Shaparova was another to fall, but there was no such drama for a rampant Rafael Nadal who powered into the last eight with a straight sets win over Tomas Berdych.

Federer was gunning for a 21st Grand Slam title but had a battle on his hands from off against the 20-year-old, touted among the new generation of young stars as a future champion.

“I’m the happiest man on Earth right now, I cannot describe it,” said the 14th seed, who is the first Greek in history to reach the quarter-finals of a Slam.

“I’ve been idolising him (Federer) since the age of six. It was a dream come true for me just being on Rod Laver facing him. Winning at the end, I can’t describe it.”

The Swiss great was gracious in defeat, saying “I lost to a better player who was playing very well, who hung in there and stayed calm”.

Nadal cruises

Nadal barrelled past former world number four Tomas Berdych 6-0, 6-1, 7-6 (7/4) to tear into the quarter-finals.

Next in the firing line is 21-year-old unseeded American Frances Tiafoe, who celebrated his 21st birthday in style by beating 20th seed Grigor Dimitrov to reach the quarter-finals of a Grand Slam for the first time.

The American world number 39 broke down in tears after stunning the Bulgarian 7-5, 7-6 (8/6), 6-7 (1/7), 7-5 in 3hr 39min.

The Spanish second seed is yet to drop a set and blasted out of the blocks to win nine games in a row against the Czech. He then brutally kept his foot on the throat to win in 2hr 5min minutes on Rod Laver Arena.

Roberto Bautista Agut came through a third five-setter to knock out 2018 finalist and sixth seed Marin Cilic in the fourth round.

The in-form Spanish 22nd seed will play in his first Grand Slam quarter-final after winning 6-7 (6/8), 6-3, 6-2, 4-6, 6-4 in two minutes under four hours on Margaret Court Arena.

“I always say the same when I am back from injury. I don’t expect negative or positive things,” said Nadal, who hadn’t played since the US Open before roaring through his first four matches in Melbourne without dropping a set.

“When you come back, you need a bit of luck at the beginning because it’s important the first couple of matches.”

“It means the world,” said Tiafoe, voice cracking. “I worked my ass off, man.”

Tiafoe is the son of immigrants from Sierra Leone and his father works as a janitor.

“I told my parents 10 years ago I was gonna be a pro tennis player and change their life,” he said. “Now I’m in the quarter-finals of a Slam. I can’t believe it.”

The in-form 22nd seed Bautista Agut began his season by beating Novak Djokovic en route to the Doha title and now faces either defending champion Roger Federer or Stefanos Tsitsipas for a place in the semi-finals.

He began his Australian Open campaign with an epic five-set win over Andy Murray, in what could be the three-time Grand Slam winner’s last match because of a chronic hip injury.

His second round match against Australian John Millman also went the full distance before a straight-sets third round win against 10th-seeded Russian Karen Khachanov.

On Sunday he ended Croat Cilic’s hopes of a repeat match-up against Federer in the quarter-finals after losing to the Swiss master in five sets in last year’s final.

Against Nadal, shell-shocked Berdych finally exerted some pressure after winning just one game in the first to sets, holding set points in the ninth and 11th games.

But the Czech, who missed five months last year with a back injury, let his frustrating day get the better of him when the serve clock mysteriously packed up during the tiebreak.

As Nadal served at 5-4, Berdych complained to the umpire about the finicky Spaniard being too slow between points.

“I don’t see (the clock) when we change over and I don’t see now,” Berdych moaned, failing to realise that all the electronic boards on the centre court had failed.

“Take as long as you want, Rafa,” shouted one fan.

Nadal, who is aiming to become the first man in the Open-era to win all four Slams twice if he can add to his 2009 Aussie crown, agreed Berdych had finally come to the party in the third set and made life tough.

Perfect birthday gift

The aggressive American upset the 20th seed in four high-quality sets that saw multiple breaks of serves and an avalanche of breathtaking winners. Tiafoe was on the front foot from the start and took the first set after 52 minutes and marked it with a one-arm raised fist salute.

Dimitrov hit back at the start of the second but double-faulted at 4-2, 30-40 to squander the early break to the consternation of coach Andre Agassi in his player box. It got worse when the 27-year-old as he blew three set points at 6-3 in the tiebreak.

Tiafoe took advantage and ripped a winner on his first set point to create a two-set cushion and then posed in admiration at his own work.

Power-packed Tiafoe squandered a break in the third and was in trouble again at 4-4, deuce until he unloaded a crosscourt forehand into the corner at deuce with such venom it almost tore the fur from the ball.

A sweet volley to go to 5-4 was met with a beaming smile to his box and the set headed for another tiebreak. Dimitrov this time raced to 6-1 and got himself back in the match on his first set point as Agassi leapt to his feet and smacked the barrier in front of him in a mixture of relief and delight.

Another attritional set ensured until at 5-5 Tiafoe, who played in the recent mixed teams Hopman Cup with Serena Williams, secured the decisive break and served out to set up a last-eight clash with number two seed Nadal on Tuesday.

After celebrating by ripping his shirt off, beating his chest and showing off his muscles, LeBron James-style, Tiafoe seemed almost embarrassed.

He admitted he will have no chance of celebrating his birthday as he will have to prepare for the daunting prospect of facing the 17-time Spanish Grand Slam champion.

“I can’t do anything tonight. He’s going to run me like crazy,” he said.

Men’s singles - 4th round

Frances Tiafoe (USA) bt Grigor Dimitrov (BUL x20) 7-5, 7-6 (8/6), 6-7 (1/7), 7-5

Rafael Nadal (ESP x2) bt Tomas Berdych (CZE) 6-0, 6-1, 7-6 (7/4)

Roberto Bautista Agut (ESP x22) bt Marin Cilic (CRO x6) 6-7 (6/8), 6-3, 6-2, 4-6, 6-4

Stefanos Tsitsipas (GRE x14) bt Roger Federer (SUI x3) 6-7 (11/13), 7-6 (7/3), 7-5, 7-6 (7/5)

With inputs from AFP