(CNN) -- World number one Serena Williams has suffered a shock defeat in the first round of the Andalucia Open in Marbella, Spain, losing in three sets to little-known Czech Klara Zakopalova.
Williams crashed out in her first clay-court match of the season in the Andalucia Open.
The American, playing her first clay-court match of the season, was beaten 6-4 3-6 6-1 by her world ranked No.95 opponent.
The 26-year-old Zakopalova, had only won two matches in 2009 before this week and she went into Wednesday's encounter having lost both of her previous meetings with Williams, failing to win a set in either match.
She will now face fellow-Czech Renata Voracova in the second round.
The defeat is Williams' second in four days following her loss to Victoria Azarenka in the final of the Miami Masters, where her peformance was severely hampered by a thigh injury which required heavy strapping.
There were no such problems for third seed Kaia Kanepi of Estonia, who reached the second round with a 6-4 6-2 win over Silvia Soler Espinosa of Spain.