MELBOURNE -- World No 1 Iga Swiatek crashed out of the Australian Open on Sunday after a shock fourth-round defeat to reigning Wimbledon champion Elena Rybakina, while men's third seed Stefanos Tsitsipas survived a major scare to reach the quarterfinals.

The upsets at an unpredictable tournament continued with hot favorite Swiatek's exit perhaps the most surprising so far.

The Pole will have to wait another year to break her title drought in Melbourne after falling to an impressive Rybakina 6-4, 6-4 in 89 minutes.

It is the first time at a Grand Slam in the Open era - since 1968 - that the top two seeds in the men's and women's draws all fell before the quarterfinals.

"I felt the pressure," said 21-year-old Swiatek, who is a three-time Grand Slam champion.

"I felt that I didn't want to lose instead of wanting to win.

"I felt like I took a step back in terms of how I approach these tournaments, and I maybe wanted it a little bit too hard."

While Swiatek was left disappointed, Kazakhstan's Rybakina took a major step towards adding a second Grand Slam title to her collection.

Moscow-born Rybakina, the 22nd seed, unleashed her high-octane game and hit 24 winners to overwhelm a flustered Swiatek.

Rybakina stormed into a quarterfinal against 2017 French Open champion Jelena Ostapenko, who also produced a boilover by defeating seventh seed Coco Gauff 7-5, 6-3.

There has been much hype over 18-year-old Gauff, who has been tipped as a successor to her legendary American compatriot Serena Williams, but the pressure appeared too great for her as she fell well short of a maiden Grand Slam triumph.

With Swiatek and second seed Ons Jabeur eliminated, red-hot American Jessica Pegula has ascended into title favoritism.

The third seed strengthened her status with a comfortable 7-5, 6-2 victory over former French Open champion Barbora Krejcikova.

Pegula made the quarterfinals of the Australian Open for a third consecutive year.

Tsitsipas, the highest seed remaining in the men's draw, overcame a gallant comeback from 15th seed Jannick Sinner 6-4, 6-4, 3-6, 4-6, 6-3.

The third seed appeared to be cruising after winning the opening two sets before the Italian stormed back to force a deciding set.

Tsitsipas rallied and gained the decisive break in the sixth game before prevailing in an epic contest lasting four hours.

"I'm trying to do my best out here. It's not easy," Tsitsipas said. "I had an unbelievable opponent on the other side of the court today, playing incredible tennis in the third and fourth sets."

Tsitsipas plays 21-year-old Jiri Lehecka, who defeated sixth seed Felix Auger Aliassime 4-6, 6-3, 7-6 (2), 7-6 (3).

"Honestly, it feels amazing," said Lehecka, who is ranked 71.

"It's tough to find the words because of what I've been through in the last year and now coming back to Australia."

Sebastian Korda, son of 1998 Australian Open champion Petr Korda, will meet 18th seed Karen Khachanov in a surprise quarterfinal match-up.

Korda, the 29th seed, upset 10th seed Hubert Hurkacz 3-6, 6-3, 6-2, 1-6, 7-6 (7), while Russian Khachanov swept aside Yoshihito Nishioka 6-0, 6-0, 7-6 (4).

Men's favorite Novak Djokovic highlights fourth-round action on Monday, while China's Zhang Shuai plays former world No. 1 Karolina Pliskova.