Defending Wimbledon champion Ashleigh Barty lost to Spain's Sara Sorribes Tormo

Ashleigh Barty

A major upset took place on the second day of the tennis women's singles bracket.

On Sunday, Spain's Sara Sorribes Tormo, who is ranked No. 48, defeated the world's No. 1-ranked Ashleigh Barty of Australia 6-4, 6-3 on Centre Court at Ariake Tennis Park. Barty's loss comes two weeks after she won women's singles at Wimbledon.

Barty, 25, finished Sunday's match with 55 unforced errors, according to the WTA.

"Really disappointing day," Barty said after her match. "And I was pretty erratic. But I'm really excited for doubles. … [I still have a chance] to do everyone proud."

Before her Olympic victory on Sunday, Sorribes Tormo had one win in the WTA from March in Guadalajara, Mexico.

Meanwhile, second-seeded Naomi Osaka swiftly won her first Olympic match on Sunday.

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Osaka, who is representing Japan, defeated China's 52nd-ranked Saisai Zheng in two sets, 6-1, 6-4. Sunday marked second-seeded Osaka's first match in two months after she decided to sit out both the French Open and Wimbledon after speaking out about her mental health struggles and being fined $15,000 in May for not participating in media requirements and press conferences.

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