Osaka, the star of the opening ceremony, defeated China's Zheng Saisai 6-1, 6-4 and said she felt "refreshed" after taking an eight-week break for mental health reasons.
apan's Naomi Osaka won in straight sets on her highly-anticipated return to the court at the Tokyo Olympics on Sunday, while world number one Ashleigh Barty crashed out in the first round.
Osaka, the star of the opening ceremony, defeated China's Zheng Saisai 6-1, 6-4 and said she felt "refreshed" after taking an eight-week break for mental health reasons.
"I felt really nervous being in Japan and playing here for the first time in maybe two years, and for it to be my first Olympics," said Osaka, chosen as the first tennis player to light the Olympic cauldron on Friday.
"It was definitely really nerve-wracking. But I am glad I was able to win, she is a very tough opponent."
The Australian Open champion had not played since May, when she walked out of Roland Garros saying that media commitments were harming her mental health.
"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," she said, in her first appearance before media.
"I feel like the break that I took was very needed, but I feel definitely a little bit refreshed and happy again."
Osaka showed few signs of rust as she reeled off the opening five games on the Ariake Coliseum centre court, which likely would have been packed to capacity if not for a spectator ban because of coronavirus restrictions.
The second seed broke the 52nd-ranked Zheng for a 2-1 lead in the second set and closed out an 87-minute victory on her third match point.
The 23-year-old Osaka is attempting to become Japan's first Olympic tennis champion. She will play Switzerland's Viktorija Golubic in the last 32.
Osaka is now the clear favourite for gold after Barty, the reigning Wimbledon champion, dropped serve twice in each set and made 55 unforced errors in a 6-4, 6-3 loss to Spain's 48th-ranked Sara Sorribes Tormo.
"I'm disappointed I wasn't able to get through today, it just wasn't my day," said Barty.
"I never really felt comfortable out there and wasn't able to play the match on my terms. I was a bit erratic and made too many errors."
Sorribes Tormo will go on to face France's Fiona Ferro in the second round.
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