Stefanos stuns Federer

Defending champion Roger Federer was stunned by fiery Greek Stefanos Tsitsipas who ended his bid for a record seventh Australian Open Sunday on a day of upsets that also saw second seed Angelique Kerber crash out.

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.

World number two Kerber was also sensationally bundled out by a woman playing the event for the first time, with American Danielle Collins humiliating the Wimbledon champion 6-0, 6-2 in under an hour.

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.

"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".

Men's second seed Nadal, returning from foot surgery, barrelled past former world number four Tomas Berdych 6-0, 6-1, 7-6 (7/4) as he stays on track for an 18th Grand Slam title.

"I always say the same when I am back for injury," said the Spaniard. "I don't expect negative or positive things. I just try to do my work every day and just be with (the) right attitude every single day."

He will play world number 39 Frances Tiafoe for a place in the semi-finals after the young American celebrated his 21st birthday by grinding his way past Grigor Dimitrov 7-5, 7-6 (8/6), 6-7 (1/7), 7-5.

Hometown hero Ashleigh Barty also made the last eight after muscling past Sharapova and will next meet Petra Kvitova.