US Open champion Naomi Osaka said she had "the worst attitude" in her loss to Lesia Tsurenko in the Brisbane International semi-finals.
The Japanese second seed was visibly frustrated as she was beaten 6-2 6-4 by Ukraine's Tsurenko in just 66 minutes.
Osaka, who won her maiden Grand Slam title in September, said the defeat had taught her "a valuable lesson".
"I was sulking a little bit, and there are moments that I tried not to do that," the 21-year-old explained.
"I feel like I didn't really know how to cope with not playing well.