(CNN) -- Defending champion Marion Bartoli has been beaten in the quarterfinals of the Bank of the West Classic in Stanford, losing in three sets to Belarusian Victoria Azarenka.
Frenchwoman Bartoli, who had won eight succesive matches in the Californian event prior to Friday's last eight clash, took the first set before the eighth seed fought back to seal a 3-6 6-3 6-3 win.
"I was in a position to win the match, but she eventually played really well and was able to come up with the victory," Bartoli told the official WTA Tour website.
Azarenka -- who celebrates her 21st birthday this weekend -- will now face top- seeded Australian Samantha Stosur, who battled past Belgian Yanina Wickmayer 7-5 3-6 6-3.
Meanwhile, Russian duo Maria Sharapova and Elena Dementieva thrilled the crowd in the night match, with fifth seed Sharapova defeating the second seed in a match that lasted two hours and 47 minutes.
Sharapova will now face third seed Agnieszka Radwanska of Poland after out- lasting her compatriot 6-4 2-6 6-3.
"I feel like I played much better than in my first round," Dementieva told the WTA website. "But my serve was not good enough and she played very well."
Radwanska defeated unseeded Russian and close friend Maria Kirilenko 7-5 6-0 in the final remaining quarterfinal.