The 20-year-old Anisimova beat the two-time Australian Open winner 4-6, 6-4, 7-6 (5) to capture one of the biggest wins of her career. She came into the tournament ranked 60th in the world.
“I knew I had to be playing sharp if I wanted to give myself a chance,” Anisimova said after the match.
Anisimova dug herself a hole after the first set but managed to bounce back in the second and play as well as she could to edge out Osaka in the third. She saved two match points in the third set, serving to stay in the match and ending with an ace.
She had 46 winners compared to Osaka’s 21.
Anisimova had previously beaten Olympic champion Belinda Bencic in the second round.
The Freehold Township, New Jersey, native is into the fourth round, where she will face the top-seeded Ash Barty. Anisimova made it to the fourth round in 2019 as well.
Barty is one of the top tennis players in the sport. But in one of the biggest tournaments of the season in front of her home crowd, she’s come up short in the last three years. She’s never won the Australian Open.
The Associated Press contributed to this report.