Serena Williams blamed a headache for her poor play in a 7-6 (5), 6-3 upset loss to qualifier Alina Jidkova in the second round of the Generali Ladies Open in Linz, Austria.
The third-seeded Williams, who got a first-round bye, made 29 unforced errors. She hadn't played in a month because of lingering pain in her left knee.
"My knee was pretty OK, but I suffered from a bad headache," Williams said. "I am really disappointed, but I felt really dizzy and was lacking energy."
Jidkova, a 25-year-old Russian ranked 73rd in the world, was asked whether she thought Williams was not at her best. "She was not fit?" she said. "She was hitting great, and I don't think she had any pains."