The world number two was knocked out 6-1 6-4 by Czech Marketa Vondrousova in her first tournament since pulling out of the French Open in May
Naomi Osaka, Japan's great hope for tennis gold, lost in the third round of the Tokyo Olympics on Tuesday, saying she had not known how to cope with the pressure of the occasion.
The world number two was knocked out 6-1 6-4 by Czech Marketa Vondrousova in her first tournament since pulling out of the French Open in May, when she said she had been suffering from depression for almost three years.
Osaka had said then she would boycott news conferences to raise awareness of players' mental well-being, but she did speak to reporters after the defeat by Vondrousova.
"I definitely feel like there was a lot of pressure, this time around," she said. "I think it's maybe because I haven't played in an Olympics before and for the first one to be here was a bit much.
"But I think I'm glad with how I played... with taking that break that I had. I've taken long breaks before and I've managed to do well.
"And I'm not saying that I did that right now, but I do know that my expectations were a lot higher than how my result was. So... I think my attitude wasn't that great, but I didn't really know how to cope with that pressure... so that's the best that I could have done in this situation.
"For me, I'm really glad to be here. I'm sad that I lost, of course, but all in all really happy with my first Olympic experience."
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Japan's Kei Nishikori, who played on Centre Court hours after Osaka, said he had not spoken to his team mate since her loss but offered his sympathies following his second-round win over American Marcos Giron.
"Very sad, of course (that) Naomi lost, and surprised. But I knew she had a lot of pressure, this is her first time Olympics and I know it's not easy," Nishikori said, adding that he would send Osaka a message via Whatsapp.
"I didn't see her match today so I cannot say much, but of course it's sad to see Naomi lost."
The women's tennis event has now lost both of its top draw cards after world number one and Wimbledon champion Ash Barty was beaten in the first round.
Osaka, who lit the Olympic cauldron on Friday to open the Games, seemed out of sorts on the Tokyo blue courts and never settled into a rhythm as Vondrousova forged ahead.
The Japanese player committed 18 unforced errors throughout the match - three times the number made by world number 42 Vondrousova.
In the quarter-finals, the Czech will face either Spain's Paula Badosa or Nadia Podoroska of Argentina, who play later on Tuesday.