Osaka, a two time Australian Open champion, had gone a set up in the high quality match on Friday but failed to close it out, with the 20-year-old Anisimova completing her comeback in a third set tie-break to win 4-6 6-3 7-6 (10-5).
“I’m speechless, I absolutely love playing in front of you guys in Melbourne. Honestly, it’s so much fun,” Anisimova said to the crowd after the match.
“I mean, I can’t stop smiling even when I’m playing, even though I should be serious.”
The first meeting between the two women produced a spectacular match with the Australian crowd cheering both players on until its conclusion.
World No. 60 Anisimova saved two match points and she continues her impressive form this season. The American will now face two-time grand slam winner Ash Barty for a place in the quarterfinals.
Barty came through her third round match against Italy’s Camila Giorgi with ease, winning 6-2 6-3.
Osaka still finding form
Osaka had breezed through her earlier round matches in Melbourne this week but faced a very different proposition in Anisimova.
The two traded powerful shots from the baseline but Osaka was unable to fully capitalize on the match points she created for herself.
It comes as the 24-year-old continues her comeback after taking a break from the sport.
She withdrew from last year’s French Open, citing mental health issues, and chose not to participate at Wimbledon.
She now has the chance to prove herself against the very best again when she faces Barty in the next round.
Meanwhile, Rafael Nadal survived a minor scare in his third round match against Russian Karen Khachanov on Friday.
Having cruised into a two-set lead, the Spaniard lost the third but recovered his form to win 6-3 6-2 3-6 6-1.