After being broken in the first game, a fan shouted "Naomi, you suck" and Osaka could later be seen wiping away tears.
After the match, the event's 2018 champion addressed the crowd on center court, saying the incident reminded her of when Venus and Serena Williams were booed at the tournament in 2001.
"I've been heckled before and it didn't really bother me," Osaka said while holding back tears.
"But being heckled here. I've watched video of Venus and Serena get heckled here and if you've never watched it, you should watch it. And I don't know why, but it went into my head and got replayed a lot."
"I just want to say thank you and congratulations," she concluded.
Osaka has been open about her struggles with mental wellness in the past and took a break from the sport following her upset loss at last year's U.S. Open. She said she was in a great place emotionally coming into the tournament.