Novak Djokovic surged into the Australian Open quarter-finals in ominous fashion on Monday while Aryna Sabalenka was an equally ruthless winner.

After a series of shocks at Melbourne Park, normal order was more or less restored on day eight, except for fourth seed Caroline Garcia bowing out under the weight of expectation.

Djokovic demolished Alex de Minaur for the loss of just five games to sweep into the last eight and step up his bid for a 10th Melbourne crown, and record-tying 22nd major title in all.

He will meet fifth seed Andrey Rublev for a semi-final berth after the Russian toppled Danish teenage talent Holger Rune in a thrilling five-set clash also at Rod Laver Arena.

The Serb's 6-2, 6-1, 6-2 triumph over 22nd-seeded home hope De Minaur was significant also because his troublesome left hamstring was much improved.

Asked afterwards how he had been so emphatic, Djokovic told the crowd: "Because I wanted to." The 35-year-old called it his "best match of this year so far" and a "perfect match".

And of his hamstring added: "Tonight I didn't feel any pain. I moved as well as I have the whole tournament. It means we are progressing in the right direction."

His next opponent Rublev admitted he was "lucky" after saving two match points against Rune in energy-sapping heat. He described beating the 19-year-old as "not like a rollercoaster, it's like they put a gun to your head. A rollercoaster is easier".

In a men's draw decimated by shocks, including the second-round exit of reigning champion Rafael Nadal, there will be a last-eight clash between two unseeded Americans.

The 20-year-old Ben Shelton, on his first trip outside the United States, emerged from another five-setter against friend and fellow American JJ Wolf.

Shelton is only the fourth man in the past 20 years to reach the Melbourne quarter-finals on debut.

"Definitely a surprise," said 89th-ranked Shelton, who a year ago was at the University of Florida and ranked 569 in the world. "It being my first time, never being out of the United States, I knew it would be a struggle," he added.

"So I think it maybe has helped me a little bit kind of not having that expectation or the feeling that I have to perform, but being able to just go out there, be myself and play free."

He plays Tommy Paul, who defeated 24th seed Roberto Bautista Agut of Spain.

In the women's draw, Garcia became the latest top-10 seed to fall, with a shock defeat to Magda Linette, ranked 45 in the world.

This is the first Grand Slam since the Open era began in 1968 to lose the top two seeds in both the men's and women's draws before the last eight.

Unseeded Pole Linette stunned Garcia 7-6 (7/3), 6-4 and the French player admitted that expectations and nerves got the better of her.

Linette said she "couldn't believe it" as she reached her first Grand Slam quarter-final at the age of 30.

She faces Karolina Pliskova after the former world number one romped past China's Zhang Shuai 6-0, 6-4.

Sabalenka never really looked like she would follow top seed Iga Swiatek, Garcia and the rest out of the first major of the year.

The Belarusian and third-seeded American Jessica Pegula -- both chasing a maiden major crown -- are now the women to beat.

Sabalenka defeated dangerous 12th seed Belinda Bencic 7-5, 6-2 to set up a last-eight clash against unseeded Donna Vekic, who beat 17-year-old Linda Fruhvirtova in three sets. (AFP)