Had my back to the wall throughout: Sharapova

Maria Sharapova wipes off the sweat in her match against Carla Suarez Navarro at the Uniprix Stadium

Montreal: Wimbledon champion Petra Kvitova and French Open winner Maria Sharapova suffered third-round shock exits while top seed Serena Williams avoided the upset bug Thursday at the WTA Montreal hardcourt tournament.

Maria Sharapova wipes off the sweat in her match against Carla Suarez Navarro at the Uniprix Stadium

Russian Ekaterina Makarova upended second-seeded left-hander Kvitova 6-4, 1-6, 6-2, while diminutive Spaniard Carla Suarez Navarro stunned fourth-seeded Sharapova 6-2, 4-6, 6-2, following a third-set rain delay, at Uniprix Stadium.

Williams advanced by defeating Lucie Safarova 7-5, 6-4 to reach the quarter-finals. Suarez Navarro, who is seeded 14th in Montreal and ranked 16th in the world, shrugged off two rain delays at the $2.4 million event and emerged with the victory over Sharapova who saw her preparations for the upcoming US Open suffer a huge setback.

"I couldn't find my rhythm from the beginning. "Always had my back against the wall throughout the whole match," Sharapova said. "It was a tough match," Sharapova said.

"I thought my opponent played a really good match. "Even though I felt like I started feeling a little bit better, it wasn't enough in the end."