A "refreshed" Naomi Osaka marked her return to competition with a confident victory in the first round of the Tokyo Olympics women's singles and her hopes of landing gold for Japan were given a boost by the shock defeat of world No 1 Ashleigh Barty.
Osaka, 23, has not competed since withdrawing after her first round match at the French Open at the start of June, citing mental health reasons and having opted to shun media obligations, but there were few signs of rust in her 6-1, 6-4 win over China's Saisai Zheng on Sunday.
"I feel like more than anything I'm just focused on playing tennis. Playing the Olympics has been a dream of mine since I was a kid," said Osaka, who is the poster athlete of the Tokyo Games and lit the Olympic torch at Friday's opening ceremony.
"I feel like the break that I took was very needed, but I feel definitely a little bit refreshed and happy again."
Any doubts over her match sharpness were immediately and emphatically answered when Osaka sent a booming serve down the tee with the very first point. From there, she broke Zheng twice to take a commanding 4-0 lead before comfortably closing out the first set to love.
There was only one break in the second set, coming in the third game, and that was all the world No 2 needed as she wrapped up the match with a love service hold.
Four-time Grand Slam champion Osaka will play Switzerland's Viktorija Golubic, the world No 50, in the last 32 and she is now the leading contender for gold after Australia's Barty was beaten 6-4, 6-3 by Sara Sorribes Tormo of Spain.
Barty entered the Tokyo Games having just clinched the Wimbledon title but an error-strewn performance, comprising 55 unforced errors, saw her slump to a surprise defeat to the world No 48.
"It's an amazing feeling, I still can't believe it," said Sorribes Tormo, who will face France's Fiona Ferro in the second round.
"It's something incredible for me. It's something that I've been dreaming of all my life, being here and even more so beating the world No 1. I'm super, super happy."
Spain will be well represented in the second round after Carla Suarez Navarro recorded her first win since returning to professional tennis following her recovery from Hodgkin Lymphoma with a 6-4, 6-1 win over Tunisia's Ons Jabeur.
Suarez Navarro, a former world No 6, was diagnosed with cancer in September last year and after getting the all-clear, returned to the tour for the French Open having previously announced her retirement shortly before her diagnosis.
Her win over Jabeur, who was riding high after winning her first WTA Tour title and reaching the Wimbledon quarter-finals earlier this summer, sets up a second round meeting with Czech Republic's fifth seed Karolina Pliskova.
Sorribes Tormo and Suarez Navarro will be joined by a third Spaniard in the second round after former world No 1 Garbine Muguruza edged Veronika Kudermetova, representing the Russian Olympic Committee, 7-5, 7-5.