It is the second time in a row that Osaka, which has won four Grand Slams, has failed to make it past the first round.
She had given up in her opening match last week at the Toronto tournament due to back pain and remains uncertain, thirteen days before the US Open which will open on August 29.
The Japanese made a lot of mistakes and only lasted 1h15 against the 44th player in the world Zhang, 33 years old.
Osaka, 24, has won only once on hard court this season.
It was for her entry into the running at Stanford at the beginning of the month against another Chinese, Zheng Qinwen (41st).
Currently 39th in the WTA rankings, the former world number one had reached the final of the Cincinnati Masters in 2020. She is far from her level this year and her form seems to be declining over the season.
After six confrontations, Osaka and Zheng are now tied, with three wins each.
"It's always difficult to play against a good friend, said Zhang Shuai, Naomi is amazing but today was not her best day".
© 2022 AFP