Naomi Osaka made a successful return to competitive tennis after two months away, while world No 1 Ashleigh Barty suffered a shock exit in the first round of the women's singles competition in Tokyo.
Osaka, who was given the honour of lighting the Olympic cauldron at the opening ceremony, defeated 52nd-ranked Zheng Saisai of China 6-1 6-4 in her first-round contest.
The 23-year-old Japanese pinup pulled out of the French Open and the Wimbledon Championships on account of protecting her mental health from having to answer questions at press conferences.
In contrast to Osaka's time away from the court, Barty arrived in Tokyo match-sharp off the back of securing a first Wimbledon title at the recent grass-court Grand Slam.
The Australian, who was making her Olympic debut, fell 6-4 6-3 to her 48th-ranked opponent Sara Sorribes Tormo and finished the match with a staggering 55 unforced errors.
The 25-year-old now focuses her attention on securing an Olympic medal in the doubles, alongside her partner Storm Sanders.
Following her first-round victory at the Ariake Tennis Park Sunday, Osaka did stop to speak to the reporters who were present.
"More than anything else I'm just focused on playing tennis," she said. "The Olympics has been a dream of mine since I was a kid, so I feel like the break that I took was very needed. I feel definitely a little bit refreshed and I'm happy again."
Osaka played the 50th-ranked Viktorija Golubic, a recent Wimbledon quarter-finalist, in the second round.