Double defending champion Sabalenka blew away Russian 17-year-old Mirra Andreeva 6-1, 6-2 in a ruthless display on the hottest day of the tournament so far.

As temperatures hit 34 degrees Celsius (93 Fahrenheit) in Melbourne, Gauff dropped a set for the first time this season but fought back to beat Belinda Bencic 5-7, 6-2, 6-1.

Sabalenka and Gauff will meet in the semi-finals should they win their respective matches in the last eight.

Belarus's Sabalenka was out on a roasting centre court for only 62 minutes before registering an 18th consecutive win at Melbourne Park.

"I'm super happy to get through this difficult match in straight sets," said Sabalenka, who faces Anastasia Pavlyuchenkova next.

The Russian 27th seed beat ailing Croatian 18th seed Donna Vekic 7-6 (7/0), 6-0.

Sabalenka struggled with her serve in colder conditions during the first week, but was untouchable as the mercury soared at the start of the second.

"The ball was flying like a rocket. I hope conditions are going to be the same till the end of the tournament," said Sabalenka.

World number three Gauff next faces Spain's 11th seed Paula Badosa, who dismantled Serbia's Olga Danilovic 6-1, 7-6 (7/2).

"I thought in the first set she played great tennis and it was tough for me to be on the offensive," American Gauff said after outlasting Bencic to extend her unbeaten streak to 13 matches going back to last year's WTA Tour Finals.

"I just played more aggressively in the second set and then also the third set. But overall, I'm happy with how I played."