The shock 2021 French Open champion is mounting a compelling case for a second slam in seven months after brushing aside injured two-time Melbourne Park winner Victoria Azarenka on Sunday.

Krejcikova gave Azarenka short shrift with a 6-2 6-2 victory on Rod Laver Arena to set up a meeting on Tuesday with resurgent American Madison Keys.

Azarenka received treatment to her neck and shoulder early in the second set and needed regular assistance from the trainer during changeovers.

Not being fully fit spelt doom against Krejcikova, who has incredibly soared to world No.4 having only cracked the top 100 for the first time last year.

Before her improbable charge to Roland Garros glory last June, the Czech had only won six grand slam singles matches since turning pro more than a decade ago.

Now Krejcikova is suddenly within three wins of another major.

"It's actually for a dream like this to play on such a court and play a champion - wow, I'm in the quarter-finals," the fourth seed said after clubbing 23 winners against Azarenka.

Keys earlier posted an equally dominant fourth-round upset win over world No.6 Paula Badosa.

Keys ran Badosa ragged in a 6-3 6-1 rout that vaulted the American into her eighth grand slam quarter-final - but first since the 2019 French Open.

A semi-finalist in Melbourne in 2015 and runner-up at the 2017 US Open, Keys had tumbled to 87th in the world before bursting back to form with a drought-breaking title triumph in Adelaide last weekend.

Seemingly free of the hamstring injury that dogged her 2021 season, the one-time world No.7 has continued her revival at the Open.

Keys barely gave Badosa a sniff.

Fresh off her own tournament success last week in Sydney last week, Badosa was also riding an eight-match winning streak.

But the Spaniard coughed up 10 double-faults under the constant strain of trying to keep pace with Keys' relentless power and precision with the match done in just one hour and nine minutes.

"I served really well and returned really well so I was able to dictate," Keys said.

"I knew I was going to have to take my chances and just got for it because I knew if I'd have give her an inch, she would take it."

American Jessica Pegula, proving somewhat of a Melbourne Park specialist, advanced to the last eight of the Open for the second successive year with a 7-6 (7-0) 6-3 win over fifth seed Maria Sakkari.

Seeded 21st this campaign after arriving as world No.61 last year, Pegula's reward is a crack at Australia's top-seeded Wimbledon champion and title favourite Ash Barty on Tuesday.

Barty qualified for her fourth straight Open quarter-final with a 6-4 6-3 win over Pegula's US compatriot Amanda Anisimova in the feature night match.

Australian Associated Press