Serena Williams continued her impressive Australian Open preparations with a straight-sets thrashing of Tsvetana Pironkova on Wednesday, as world No 3 Naomi Osaka and top-ranked Ashleigh Barty struggled.
Williams, 39, has been in belligerent form at the Yarra Valley Classic and overpowered the Bulgarian with a 6-1, 6-4 victory in 74 minutes.
Williams, aiming for a record-equalling 24th Grand Slam title at the Australian Open, broke Pironkova first up and kept her foot on the gas with 25 winners and six aces.
The American will play world No 6 Karolina Pliskova or compatriot Danielle Collins in the quarter-finals.
"So far, so good. It's special to play here with what's going on in the world," said Williams, who only lost four games against Daria Gavrilova in her opener on Monday.
Osaka and Barty, however, were pushed to the brink, but both avoided early exits at Melbourne Park.
Japan's Osaka was made to work hard against in-form Katie Boulter, but fought back for a 3-6, 6-3, 6-1 victory to reach the quarter-finals in the Gippsland Trophy.
She next meets Irina-Camelia Begu from Romania. "Today was really tough for me. It just felt like a new experience playing here again after such a long while," Osaka said.
"For me, I thought she played really well. I sort of had to raise my level, kind of go within myself."
British world No 371 Boulter, who knocked out Coco Gauff Tuesday, ran her error-prone opponent ragged to claim the first set in 39 minutes.
A refocused Osaka lifted her intensity to run away with the contest in a one-sided third set.
The three-time Grand Slam champion had comfortably beaten France's Alize Cornet in straight sets on Tuesday in her first competitive match since lifting her second US Open title in September.
World No 1 Barty also had a fright in her match against Marie Bouzkova of the Czech Republic, but recovered from a second-set stutter to win 6-0, 4-6, 6-3.
"Mid-match I lacked execution ... but happy to get it on my terms in the end," Barty said after a quick turnaround, having beaten Ana Bogdan in straight sets on Tuesday night.
.@serenawilliams advances in Melbourne!
— wta (@WTA) February 3, 2021
Defeats Pironkova 6-1, 6-4 to move into the last 8. #YarraValleyWTA pic.twitter.com/2KbmFyXN2J
Barty, hoping to break her country's 43-year singles title drought at the Australian Open, will face Shelby Rogers of the United States next.
Reigning Australian Open champion Sofia Kenin was also pushed hard by American Jessica Pegula, dropping the first set and finding herself 4-1 down in the second before prevailing 5-7, 7-5, 6-2.
"I was happy the way I was able to change things in the second set... I found my groove," said Kenin, who will play Garbine Muguruza next in a rematch of last year's Australian Open final.
World No 5 Elina Svitolina also had to come from behind to beat 2017 French Open champion Jelena Ostapenko 6-7, 6-3, 6-2.
She will now face 20th-ranked Belgium's Elise Mertens, who knocked out Caroline Garcia of France 7-6, 6-3.
But world No 2 Halep, like Williams, bucked the trend and downed Laura Siegemund in straight sets to set up a Gippsland Trophy quarter-final against Russia's Ekaterina Alexandrova, who upset French Open champion Iga Swiatek 6-4, 6-2. "I'm really happy with both matches, so it's good to be back," said Halep.
The World No.1 advances to the #YarraValleyWTA quarterfinals!@ashbarty defeats Bouzkova 6-0, 4-6, 6-3. pic.twitter.com/NHrr9kq26L
— wta (@WTA) February 3, 2021
