Naomi Osaka of Japan serves against Marketa Vondrousova of the Czech Republic on Tuesday in Tokyo. Photo: VCG

Japanese tennis star Naomi Osaka conceded the pressure of trying to win an Olympic gold at home was a "bit much" after a 6-1, 6-4 defeat to Marketa Vondrousova ended her title dreams on Tuesday.

Osaka, who lit the Olympic cauldron and was one of the faces of the Games, struggled in an ­error-strewn display that blew the draw wide open after the earlier exits of world No.1 Ashleigh Barty and third seed Aryna Sabalenka.

"How disappointed am I? I mean, I'm disappointed in every loss, but I feel like this one sucks more than the others," said the four-time Grand Slam winner.

Asked what went wrong, she replied, "­Everything - if you watch the match then you would probably see. I feel like there's a lot of things that I counted on that I couldn't rely on today."

The third-round defeat followed a turbulent few months for Osaka, who abandoned her French Open campaign in May after refusing to attend press conferences, citing the need to preserve her mental health.

Osaka also skipped Wimbledon, saying she had been battling depression and anxiety, before returning in Tokyo for her first Olympics, including her starring role at the opening ceremony.

But ultimately the sky-high expectations placed on the world's highest-paid female athlete proved tough to handle.

"I definitely feel like there was a lot of pressure for this. I think it's maybe because I haven't played in the Olympics before and for the first year [it] was a bit much," said Osaka.

After looking assured in the first two rounds after her eight-week hiatus, Osaka made a dreadful start under the centre court roof at a rain-hit Ariake Tennis Park and never recovered.

She dropped serve five times against the 42nd-ranked Vondrousova, who will face Spain's Paula Badosa in the quarterfinals.

"I've taken long breaks before and I've managed to do well," Osaka said. "I'm not saying that I did bad right now, but I do know that my expectations were a lot higher.

"I feel like my attitude wasn't that great because I don't really know how to cope with that pressure so that's the best that I could have done in this situation."

Ukrainian fourth seed Elina Svitolina, the highest-ranked women's player left in the competition, recovered to defeat Greece's Maria Sakkari 5-7, 6-3, 6-4.

Wimbledon runner-up Karolina Pliskova, seeded fifth, slumped to a 6-4, 6-2 loss to Italy's Camila Giorgi.

Earlier, men's third seed Stefanos Tsitsipas advanced to the third round as he avenged last month's Wimbledon loss to Frances Tiafoe, winning 6-3, 6-4.