American beats two-time winner in Australian Open Anisimova
Amanda Anisimova, 20, of the United States, defeated the defending champion in three sets on Friday.
she beat the four-time major champion 4-6, 6-3, 7-6 (5) Friday.
Anisimova understood she had to step up her game after dropping the opening set.
Anisimova saved two match chances in the third set, serving to win. She had 46 against Osaka's 21.
Despite trading strong baseline strokes, Osaka was unable to completely capitalise on her match points.
She withdrew from the French Open last year due to mental health difficulties and skipped Wimbledon.
After losing to Leylah Fernandez in the US Open in September, she took another indefinite sabbatical.
She will now meet Barty in the following round to prove herself against the best.
Azarenka honoured her son and cited her own highlights.