Tokyo,  Four-time Grand Slam winner Naomi Osaka's bid for a gold medal in her home country ended quickly on Tuesday with the world No. 2 being ousted by Marketa Vondrousova of the Czech Republic 6-1, 6-4 in the third round of the Tokyo Olympic Games here.

Naomi was competing in her first event since pulling out of the French Open in May.

"I've taken long breaks before, and I've managed to do well," Naomi said after the loss. "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."

The top three seeds, Australia's Ashleigh Barty, Belarus' Aryna Sabalenka and Naomi, have all fallen early at the Olympics. No.4 Elina Svitolina of Ukraine, a 5-7, 6-3, 6-4 winner over No.14 Maria Sakkari of Greece on Tuesday, is the highest seeded player in the tournament.

After falling to Marketa, Naomi said she understood the pressure at these Games.

"I think it's maybe because I haven't played in the Olympics before and for the first year [it] was a bit much," she said. "I think I'm glad with how I played, with taking that break that I had."

Also on Tuesday, Switzerland's Belinda Bencic, the No.9 seed, defeated No.8 Barbora Krejcikova of the Czech Republic 1-6, 6-2, 6-3 to reach the quarterfinals. It was only the second loss for Barbora in her past 24 matches.

Belinda's opponent in the quarterfinals will be No.13 Anastasia Pavlyuchenkova of ROC, who beat Spaniard Sara Sorribes Tormo 6-1, 6-3.

Camila Giorgi of Italy also pulled off an upset, as the defeated No.5 Karolina Pliskova of the Czech Republic, 6-4, 6-2 in 75 minutes.

Garbine Muguruza, the No.6 seed, defeated Alison van Uytvanck of Belgium 6-4, 6-1 to secure her fourth win in five tries against the Belgian.

Paula Badosa made it two Spaniards in the quarterfinals. She eliminated Argentina's Nadia Podoroska, 6-2, 6-3 in an hour and 24 minutes.

No.15 seed Elena Rybakina of Kazakhstan completed the quarterfinal lineup as she beat Donna Vekic of Croatia, 7-6(3), 6-4.

Quarterfinal matchups:

Anastasia Pavlyuchenkova (ROC) vs Belinda Bencic (SUI)

Elena Rybakina (KAZ) vs Garbine Muguruza (ESP)

Camila Giorgi (ITA) vs Elina Svitolina (UKR)

Paula Badosa (ESP) vs Marketa Vondrousova (CZE)