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Serena Williams says she will take some time away from tennis after being shocked by Slovakian Jana Cepelova at the Family Circle Cup.
The world number one - a three-time winner of the WTA Premier event - had no answer for 20-year-old Cepelova, who registered a stunning 6-4 6-4 victory on Tuesday.
Cepelova, ranked number 78 in the world, won the first five games of the match to take control and although the American initially responded, she could not prevent an upset.
Williams won the Sony Open for a seventh time on Saturday but did not use the quick turnaround as an excuse.
"Obviously things didn't go great out there, but she was a great counter-puncher today and hit a lot of balls back," Williams said.
"I really knew nothing about her game going into the match, so she played a really good match against me today.
"And it just wasn't my day - it just wasn't meant to be today.
"I'm going to go on a vacation, for sure. I need some time off. I just need to take a deep breath and regroup, and I think it will actually help me for the rest of the clay court season coming up.
"All credit to her. She did well today. She just tried really hard out there, and she played the best she can probably play.
"And I've made this transition (between tournaments) many, many times before, so there's really no excuse. It just wasn't my day today."