Unseeded Osaka crunched 12 aces and 24 clean winners past Barty on Saturday to send Australia's last women's singles hope packing with a crushing 6-4 6-2 third-round defeat.
Osaka's reward is a shot at world No.1 Simona Halep for a place in a grand slam quarterfinal for the first time.
"I feel really happy but I'm also kind of sorry because I know you guys wanted her to win," the 20-year-old told the Australian crowd on Margaret Court Arena.
"So thank you very much because I've never played in an atmosphere like this before. I've always wanted to play against an Australian player because on TV it always seems really cool."
The marquee match had been scheduled for Rod Laver Arena, to start not before 3.30pm.
But with Halep needing almost three-and-a-quarter-hours to subdue American Lauren Davis 4-6 6-4 15-13, and then the men's showdown between Alexander Zverev and Hyeong Chung also going the distance over five sets, Open officials shifted Barty and Osaka.
That was no problem for Osaka.
"I just think there would have been a lot more people cheering for her," she said. "So I think it was good for me."