Osaka said she appreciated taking time away from the court ahead of the Games in Tokyo, where she was chosen to light the Olympic cauldron at the opening ceremony on Friday night.
"More than anything, I'm just focused on playing tennis," she said in her first appearance in front of media in more than two months.
"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. But I feel definitely a little bit refreshed and happy again."
Osaka's return to the game was hailed by the Japanese public, who showered her with praise following her win.
"(I admire) her powerful nature. Not just when she's playing, but she has her own principles which is wonderful," said 63-year-old office worker Yoshihiro Ohba.
Osaka was in ominous form against the 52nd-ranked Zheng, racing through the first set in just 32 minutes.
In the second set, the 23-year-old gained another early break but squandered two match points on the Chinese player's serve at 5-3.
Osaka went on to serve out the match to love.