Naomi Osaka and Serena Williams survive scares to reach Australian Open last eight

Serena Williams reacts after winning a point against Aryna Sabalenka during their Australian Open match. EPA

Naomi Osaka saved two match points and Serena Williams recovered from losing her first set of the tournament as they fought their way into the Australian Open quarter-finals on Sunday.

Japan's Osaka edged a thriller with fellow major-winner Garbine Muguruza and Williams came through a physical test against Aryna Sabalenka to maintain her bid for a record-equalling 24th Grand Slam title.

Unheralded Russian debutant Aslan Karatsev extended his fairytale run, and Taiwan's Hsieh Su-wei, 35, reached the last eight for the first time after 16 years of trying.

Later, all eyes will be on whether eight-time winner Novak Djokovic can recover from a serious abdominal injury in time for his night match with Milos Raonic, last up on Rod Laver Arena.

Second seed Simona Halep will also be looking for revenge against Polish teenager Iga Swiatek, who beat the Romanian easily on the way to a maiden Grand Slam title at Roland Garros last year.

In an empty Rod Laver Arena, with fans barred on the second day of a five-day, state-wide coronavirus lockdown, Osaka was on the verge of elimination at 3-5, 15-40 on her serve in the third set.

But the three-time major champion rattled off four points in a row and then twice broke Muguruza's serve to prevail 4-6, 6-4, 7-5.

"I felt like I was intimidated because she was playing so well," said Osaka, after her first meeting with last year's beaten finalist.

"On the stressful points, I had to play within myself."

Williams, 39, was also meeting Sabalenka for the first time and she had to weather an onslaught from the Belarusian to reach the last eight 6-4, 2-6, 6-4.

"I knew it wasn't going to be easy, she was teeing off on every shot," said the American, who was on upset alert before rallying to take a tight third set.

Earlier Taiwan's Hsieh became the oldest player to make a last-eight debut in the Open era after winning 6-4, 6-2 against Czech Marketa Vondrousova, who is 14 years her junior.

"I try to pretend I'm only 18 years old," said Hsieh, who made her Slam debut in 2005 and is playing her 38th major.

Karatsev also claimed a slice of history as he became the first player in 25 years to reach a Grand Slam quarter-final on debut, stunning 20th seed Felix Auger-Aliassime in five sets.

The 27-year-old, a virtual unknown before the tournament started, battled back from two sets down to upset the Canadian 3-6, 1-6, 6-3, 6-3, 6-4.

"It took me two sets to find a way how to play," Karatsev said. "In the end I got into the rhythm in the third and fifth."

Djokovic has been given the maximum amount of time to recover from a midriff muscle tear that left him grimacing during his attritional, five-set win over American Taylor Fritz late on Friday.

Djokovic, who chose not to practise on Saturday to seek medical advice and treatment, said he couldn't guarantee he'd be able to face Raonic in the late match.

Swiatek, 19, will open the night session against Halep, after hammering the two-time Grand Slam champion for the loss of just three games in the French Open's last 16.

US Open champion Dominic Thiem -- who came from two sets down to beat Nick Kyrgios and silence a vociferous crowd -- also faces Bulgarian 18th seed Grigor Dimitrov in a fan-free Rod Laver Arena.