Naomi Osaka said she had been overwhelmed by the pressure of defending her Australian Open title and admitted she does not have a "champion mentality" after losing to 15-year-old Coco Gauff on Friday.
The 22-year-old Japanese made the startling admission after a surprise 6-3, 6-4 third-round defeat to the unseeded American, a loss she said she took "very personally".
The third seed said that she "loved" Gauff, but added: "You don't want to lose to a 15-year-old."
There was intense interest in the build-up to their second ever match, which was touted as a glimpse into the future of women's tennis.
Two-time Grand Slam champion Osaka crushed a tearful Gauff in the US Open third round, but the teenager -- the youngest player in the Melbourne draw -- got emphatic revenge.
"I don't really have the champion mentality yet, which is someone that can deal with not playing 100 percent (but still win)," said Osaka.
"And I have always wanted to be like that, but I guess I still have a long way to go.
"It's just something that I think some people are born with and some people have to have really hard, trials and stuff, to get it."
Osaka, who has spoken openly about her struggles with nerves, told reporters she had not dealt well with the "hype" leading into the match or the expectations placed on her as defending champion.
"I feel like I get tested a lot. Like life is just full of tests and, unfortunately for me, my tests are tennis matches and you guys see them," she said.
"So I just have to find a way to navigate through it.
"I feel like there are moments where I can handle them and you guys see that.
"Then there are moments like this where I get overwhelmed and I don't really know what to do in the situation."
Osaka said that she was particularly disappointed by her failure to win in front of her watching parents.
"You don't want to lose to a 15-year-old," the Japanese said.
"But I guess that's for me a reality check.
"It doesn't really matter the age of the opponent."