Former world number one Maria Sharapova suffered a setback on her return from injury when she lost 6-4 6-3 to Lucie Safarova in the first round of the Madrid Open on Sunday.
Russian Sharapova, the 11th seed, was playing her first tournament since pulling out of the Sony Ericsson Open in March with an elbow injury.
Safarova, who beat world number two Caroline Wozniacki in Stuttgart last month, broke Sharapova's serve four times on the clay and the Czech is on course for a possible last-16 clash with sixth-seeded Russian Elena Dementieva.
"If you win against these top players, as I have the last couple of months, then you get your confidence and you realise you can be up there," the world number 35 told a news conference.
"My dream is to be top 10 and it's a lot about believing in yourself."