Naomi Osaka has no regrets about her stunning third-round loss against Swiss wildcard Jil Teichmann at the Western & Southern Open on Thursday.

The four-time Grand Slam champion went down 3-6, 6-3, 6-3 against the world No. 76 and admitted that her third-round loss at the Tokyo Olympics was on her mind.

"I was doing all I was supposed to do," the world No. 2, said. "In the second and third sets, I was too defensive.

"I learned a lot from this match — I can sleep at night."

Osaka lost to an opponent who has struggled with several injuries this season but is healthy again.

"I knew inside I had this level and I was able to show it on court," Teichmann said. "This week things are working out. I needed to be patient and here I am."

Osaka stayed lowkey throughout the postmatch media session, answering questions and seeming to meekly accept the loss in her final tuneup for the U.S. Open, which begins August 30.

"I have high expectations of myself, but there was nothing more I could do to win this match," Osaka said.

"I'm almost glad I lost as it gives me so many things to work on in my game. I just hope the results come in time for the US Open."

Osaka said her only regret was not winning more than $24,200 in prize money to donate to the earthquake recovery effort in Haiti, her father's homeland.

"I'm happy, but sad that I didn't go further," Osaka said. "But I think I raised awareness. I'm glad we were able to contribute something."

Tournament officials said they would match her donation after Osaka promised to give all of her prize money to the cause.

Teichmann took just over two hours to defeat Osaka, breaking the Japanese star six times, including three times in the final set. Osaka made 41 unforced errors while hitting only 17 winners, while Teichmann struck 21 winners against 29 unforced errors.

"Literally, I'm shaking right now," Teichmann said after the match.

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