An injury-hampered world number one Serena Williams suffered a shock 6-4, 3-6, 6-1 defeat to Klara Zakopalova of the Czech Republic in the first round of the Andalucia Tennis Championships on Wednesday.
The top seed had clearly not recovered from a thigh problem that affected her performance in Miami last week and was broken seven times by Zakopalova, ranked 95 in the world.
Williams lost to Belarussian teenager Victoria Azarenka in the final of the Sony Ericsson Open on Saturday and said she was sad to have failed in her opening match on the clay in Marbella in southern Spain.
"I was trying to play my best tennis but the injury prevented me from reaching my top level," the American, who wore heavy strapping on her left thigh, said at a news conference.
World number four and second seed Jelena Jankovic thrashed Italy's Francesca Schiavone 6-2, 6-1 in their first-round clash in Marbella on Tuesday.