Serena Williams sounded a warning for her fellow Australian Open contenders on Wednesday with a sleek 6-1, 6-4 victory against Bulgarian Tsvetana Pironkova to reach the quarter-finals of the Yarra Valley Classic in Melbourne.
After top two seeds Ash Barty and Sofia Kenin faced steep challenges to keep their preparations on course, Williams put up a contrasting show at Melbourne Park's Margaret Court Arena in the evening session.
World number one Barty, who won 6-0, 4-6, 6-3, showed no signs of fatigue from having played a late match on Tuesday and started in top gear against Marie Bouzkova at the Margaret Court Arena before her Czech opponent staged a fightback.
Australian Open champion Kenin, seeded second, appeared headed for an exit against fellow American Jessica Pegula when she fell 3-0 back after losing the first set but the feisty 22-year-old found her range and rallied for a 5-7, 7-5, 6-2 win.
Williams, a 23-time Grand Slam winner and a seven-time Australian Open champion, moved well, looked composed and mixed power with poise against Pironkova, who had won a set off her during last year's US Open quarter-finals.
The 39-year-old American did not allow her a foothold in Wednesday's match and hit 25 winners against the seven managed by Pironkova, who like Williams returned to professional tennis after becoming a mother.
"It's definitely nice to get another win," Williams, who will next face Czech Karolina Pliskova or Danielle Collins for a semi-final spot, said during her on-court interview.
"She's clearly a great player, so it wasn't easy, but it was good to come through."
Barty, Australia's best hope for a Grand Slam champion this month, punished Bouzkova's weak serve to hand her a bagel in the opening set but the world number 52 showed she had the stomach for a fight by levelling the match with a break in the second.
Bouzkova and Barty traded two breaks of serve at the start of the decider before the top seed got the crucial break in the eighth game and sealed the encounter on her first match point with a booming serve.
"Coming off a night match, I had to get used to going to bed quite late again," Barty, who hit 42 winners to her opponent's 17, said. "I'm an early riser, so I didn't get a hell of a lot of sleep last night, but it's fantastic to be back out here.
"It was a really solid match. I felt like I pressed a little bit in the middle and lost my execution."
The 2019 French Open champion will next face American Shelby Rogers, who ousted Croatia's Petra Martic 7-6(1), 6-3.
Kenin, ranked fourth in the world, struggled with her unforced errors in the first half of the match but once she managed to land the ball closer to the lines, a bewildered Pegula faded away.
The Russian-born Kenin hit 14 winners more than her opponent in the match while committing 10 extra unforced errors and converted her third match point with a wide serve to set up a last eight clash against Spaniard Garbine Muguruza.
It will be a repeat of last year's Australian Open final when Kenin rallied to beat two-time major winner Muguruza, who defeated Anastasia Pavlyuchenkova of Russia 6-1, 6-2.
Osaka, Halep into Gippsland last eight
US Open champion Naomi Osaka extended her winning streak to 13 matches but only after riding out a stiff challenge from Katie Boulter to beat the Briton 3-6, 6-3, 6-1 and reach the quarter-finals of the Gippsland Trophy.
Top seed and world number two Simona Halep later had a more routine passage into the last eight of the Australian Open warm-up with a 6-2 6-4 win over German Laura Siegemund.
French Open champion Iga Swiatek crashed out of the tournament with a 6-4, 6-2 loss to Russian Ekaterina Alexandrova, while British fifth seed Johanna Konta was edged 4-6, 6-7(10), 6-7(4) by Romanian Irina-Camelia Begu in a Court Seven marathon.
Osaka is playing her first WTA tournament since securing her second title at Flushing Meadows in September and said she was grateful for Wednesday's workout after a comfortable win over Alize Cornet in her season-opener on Tuesday.
"I couldn't have asked for a better preparation match," Osaka, the second seed, told reporters.
"That's something I couldn't practice. So I'm very happy with how it went, actually. Even though it was long, I think there are a lot of things that I learned in this match."
Boulter beat American Coco Gauff in the second round and another upset looked on the cards when she matched Osaka's power-hitting to take the opening set on Margaret Court Arena.
Osaka raced to a 3-0 lead in the second set but the 24-year-old Briton would not fold and had break points to put the stanza back on serve.
The 2019 Australian Open champion upped her return game to level up the match before running away with the third set and sealing a last eight tie against Begu.
Third seed Elina Svitolina also came from behind to see off Jelena Ostapenko 6-7(4), 6-3, 6-2 and set up a quarter-final date with Belgian Elise Mertens.
Halep looked every inch the Grand Slam champion in the opening set of her match against Siegemund but lost her way when her serve faltered and she was broken at the start of the second.
The Romanian, whose last official tournament was the French Open last October, spent some time muttering to herself on the baseline but regathered her composure and broke the German twice to secure the victory.
"I'm really happy with my victory today and I'm happy to be back here," the former French Open and Wimbledon champion said.