It was Osaka’s first tournament after withdrawing from the French Open in June, when she revealed she had “suffered long bouts of depression” since winning her first Grand Slam title in 2018.
“I think I’m glad with how I played, with taking that break that I had,” she said.
“I’ve taken long breaks before and I’ve managed to do well.
“I’m not saying that I did bad right now, but I do know that my expectations were a lot higher.
“I feel like my attitude wasn’t that great because I don’t really know how to cope with that pressure so that’s the best that I could have done in this situation.”
Following impressive wins in the first two rounds, Osaka looked to be shaping up nicely for a gold-medal bid but produced 32 unforced errors in a rusty performance against former French Open finalist Vondrousova.