Brisbane - Reigning US Open champion Naomi Osaka said her poor attitude cost her during her 6-2, 6-4 loss to Lesia Tsurenko in Saturday's Brisbane International semi-finals.
Osaka went into the match as firm favourite but looked flat from the outset as Tsurenko raced through the match in just 65 minutes.
The Japanese star, who burst to prominence with her eventful US Open final win over Serena Williams, made 26 unforced errors and was broken three times in a disappointing display.
She said after the match that she didn't know how to cope once things started to go against her.
"If I'm being really frank, I just feel like I had the worst attitude today," she said.
"I feel like I didn't really know how to cope with not playing well.
"I was sulking a little bit, and like there are moments that I tried not to do that, but then the ball wouldn't go in, and then I would go back to being, like, childish and stuff.
"I feel like last year I did a lot of that," she added.
"I'm trying to change it more, and I think I have."
But Osaka said Saturday's loss was probably a better learning experience than if she had made the final.
"I think today I learned... what I can do to improve the situation," she said.
The 29-year-old Tsurenko, who will now rise to a career-high world ranking of 24, said she had adopted a new game plan during the off-season.
"I feel better with my serve and that I am moving well," she said.
"I feel more strong now, so I can kind of handle every kind of pressure on court, even when someone like Naomi is playing really strong.
"I can really stay there and I can be aggressive also."
Tsurenko will play either fifth seeded Czech Karolina Pliskova or Croatia's Donna Vekic in Sunday's final.
Results of matches played at the ATP/WTA Brisbane International at the Queensland Tennis Centre on Saturday (X denotes seed):
Kei Nishikori (JPN X2) bt Jeremy Chardy (FRA) 6-2, 6-2
Lesia Tsurenko (UKR) bt Naomi Osaka (JPN X2) 6-2, 6-4