The defending champion conceded only four points in the first four games Wednesday and rifled forehand winners seemingly at will as she breezed to 6-0 in a mere 20 minutes.
The second set started with Brengle celebrating a service hold like she'd finished a long-distance race, but gradually the No. 54-ranked American ground down Osaka to a stage in the seventh game where she finally converted a break-point opportunity -- after missing her first nine chances.
That triggered a change in the former No. 1-ranked Osaka, who responded by breaking back immediately and winning the last nine points to complete a 6-0, 6-4 victory. She finished with 37 winners and 32 unforced errors.
Osaka won the Australian Open last year, her fourth Grand Slam title, but then withdrew from the French Open and skipped Wimbledon as she took a break for her mental health. She then was ousted early at the US Open.
After a long offseason to reset, she is unbeaten in five matches in Australia this year.
Asked how she rated her form, Osaka said that's not how she's approaching things.
"Honestly I'm trying not to do that,'' she said in an on-court TV interview. "I'm a bit of a perfectionist. If I compare myself with the past, I'll never be satisfied.
"The goal for me is just to have fun ... [and] I think we're accomplishing that.''
Since the draw for the first major of the year was made, a big focus has been on a potential encounter between Osaka and Barty, the 2021 Wimbledon and 2019 French Open champion who is aiming to be the first Australian woman since 1978 to win her home championship.
Barty was front and center when the tournament celebrated its inaugural First Nations Day, albeit only for 52 minutes as she beat 142nd-ranked qualifier Lucia Bronzetti 6-1, 6-1.
"It was nice for me to be a part of it in a way that I feel most comfortable,'' Barty, who has Indigenous heritage, said of the day dedicated to the Aboriginal and Torres Strait Islander people of Australia. "Out on the tennis court is how I express myself as an athlete, it's how I'm able to express myself as a person as well.
"On a day we're bringing cultures together, bringing people together ... it was great for me to be able to play a small role doing what I love.''
Also Wednesday, French Open champion and fourth-seeded Barbora Krejcikova set up a third-round match against No. 26 Jelena Ostapenko, advancing along with No. 5 Maria Sakkari, No. 8 Paula Badosa and No. 15 Elina Svitolina, who next plays two-time Australian Open champion Victoria Azarenka.
Svitolina was leading 6-3, 5-7, 5-1 when Harmony Tan retired with a left leg injury, and waited on court until Tan was removed in a wheelchair.
"It's always horrible when any athlete gets injured in competition. She played really well and she made it not easy for me,'' Svitolina said. "It's tough to see a player going out like this.''
The Associated Press contributed to this report.