World number one Ashleigh Barty was stunned by Sara Sorribes Tormo of Spain in the first round of women's Olympics singles in Tokyo. Australian Barty, who won her second Grand Slam title at Wimbledon in July, cut a frustrated figure in her 6-4 6-3 loss to 48th-ranked Sorribes Tormo. The victory is the biggest of Sorribes Tormo's career. Japan's second seed Naomi Osaka cruised past Saisai Zheng of China 6-1 6-4. Osaka, who lit the Olympic flame in the opening ceremony, is the highest-ranked player remaining in the draw. Barty will still compete in Tokyo after she and Storm Sanders reached the second round of the women's doubles on the first day. She put in an error-strewn performance against Sorribes Tormo, making 55 unforced errors to the Spaniard's 13. "It's something I've been dreaming all my life, being here and, even more, beating a number one," Sorribes Tormo said. "It's an amazing feeling. I still can't believe it."