Two days after lighting the cauldron at the Opening Ceremony -- a moment she called "the greatest athletic achievement and honor" of her life -- Osaka took to the tennis court for her first game in almost two months on Sunday, defeating China's Saisai Zheng 6-1 6-4 on Ariake Tennis Park's Centre Court.
Wimbledon champion Ashleigh Barty's surprise loss against Sara Sorribes Tormo earlier on Sunday means Osaka is now the top-ranked player in the women's draw in her bid to become the first Japanese woman to win an Olympic tennis medal.
The four-time grand slam champion hadn't played since withdrawing from the French Open at the end of May, which followed her decision not to undertake media duties for mental health reasons.
She chose not to play in Wimbledon, too, but has arrived in Tokyo rejuvenated and ready to make her mark.
"This, playing the Olympics, has been a dream of mine since I was a kid, so I feel like the break I took was very needed," the 23-year-old Osaka told reporters. "I feel definitely a little bit refreshed and happy again."
Extreme heat and humidity has proved a challenge for tennis players in Tokyo and Osaka's match took place in baking, midday heat, broken occasionally when a light breeze swept across the court.
Her entrance was greeted by an enthusiastic stadium announcer and a smattering of applause from the near-empty stands, which mainly comprised teammates, officials and members of the media.
Despite her absence from the tour, Osaka showed few signs of rustiness as she opened her Olympic campaign, cruising through the first game with three aces, before twice breaking Zheng to race into a 4-0 lead in the first set.
World No. 52 Zheng, who is appearing in her second Olympics, had opportunities to break back in the fifth game, only for Osaka to hold on and wrap up the first set in just 32 minutes.
That dominance continued into the second set as Osaka secured another early break of serve, but this time Zheng was able to build more of a foothold and had two break points to level the set at 4-3.
It proved to be only a glimmer of hope, however, as Osaka bounced back to take the game and, shortly afterwards, the match.
"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. "It was definitely really nerve-wracking. But I am glad I was able to win, she is a very tough opponent."