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 British world number 14 Johanna Konta or Irina-Camelia Begu from Romania as she ramps up preparations for the Australian Open starting Monday.
“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.
“I was actually more calm after losing the first set because I felt like for me, I just wanted to be able to play well,” she added.
British world number 371 Boulter, who has impressed in Melbourne and knocked out teenage sensation Coco Gauff Tuesday with a comeback three-set victory, ran her error-strewn 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 number one 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 in just over two hours.
“Mid-match I lacked execution … but happy to get it on my terms in the end,” she said.
It was a quick turnaround for Barty, who beat Ana Bogdan in straight sets on Tuesday night, but she showed no ill effects to cruise through the first set in 32 minutes.
Barty’s radar went awry with 13 unforced errors in the second set and the world number 52 broke in the fifth game before levelling the match.
Barty continued to struggle on serve in the deciding set but held on to reach the quarter-finals of the Yarra Valley Classic.
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.
Defending Australian Open champion Sofia Kenin was also pushed hard, taken to three sets by American Jessica Pegula before prevailing 5-7, 7-5, 6-2.
World number four Elina Svitolina was another who struggled and had to come from behind to beat 2017 French Open champion Jelena Ostapenko 6-7 (7/4), 6-3, 6-2.
She’ll next face world number 20 Elise Mertens, who knocked out Caroline Garcia of France with a 7-6 (7/1), 6-3 victory.
Serena Williams and world number two Simona Halep are in action later Wednesday.
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