CINCINNATI: World number two Naomi Osaka suffered one of her worst losses this season on Thursday, falling to Jil Teichmann in a third-round match at the ATP and WTA Cincinnati Masters.

The 76th-ranked Swiss took the biggest upset victory of her career, defeating four-time Grand Slam champion Osaka by 3-6, 6-3, 6-3 at the final major US Open tuneup tournament.

Teichmann took just over two hours to defeat Osaka, breaking the Japanese star three times in the final set to reach the quarter-finals.

Osaka made 41 unforced errors in the match while hitting only 17 winners while Teichmann struck 21 winners against 29 unforced errors.

Reigning US and Australian Open champion Osaka lost in the third round at the Tokyo Olympics.

This was her first event outside her homeland since withdrawing from the French Open after the first round, saying taking questions from reporters after matches was causing mental issues. She skipped Wimbledon as well.

Osaka, who had a first-round bye at Cincinnati, struggled but captured her opening match, defeating American Coco Gauff 4-6, 6-3, 6-4 on Wednesday.