ROME, May 17 (UPI) -- No. 2 seed Maria Sharapova Thursday advanced to face Venus Williams in the quarterfinals of the Italian Open, but No. 1 Victoria Azarenka is out due to injury.
Azarenka said she injured her right shoulder in a 6-1, 6-2 second-round win over Shahar Peer, handing 14th-seeded Dominika Cibulkova a walkover into the quarterfinals.
Sharapova survived a seesaw battle with Ana Ivanovic 7-6 (7-4), 6-3. There were six service breaks in the second set but Sharapova's break in the seventh game put her ahead to stay.
The Williams sisters also earned spots in the quarterfinals. Wild card Venus Williams posted a 6-4, 6-3 upset of fifth-seeded Samantha Stosur. Venus Williams dropped her serve four times but countered that with six breaks. Serena Williams, the No. 9 seed, didn't lose her serve in a 6-3, 6-1 win over Anabel Medina Garrigues.
Also Thursday, No. 4-seeded Petra Kvitova edged Sorana Cirstea 6-2, 5-7, 6-2; eighth-seeded Li Na topped Chanelle Scheepers 7-6 (7-3), 6-3; and No. 12-seeded Angelique Kerber beat Julia Goerges 6-4, 6-1.
Flavia Pennetta routed Petra Cetkovska 6-0, 6-1. Pennetta won the first 11 games and then lost her serve at love as Cetkovska avoided the shutout.
Pennetta earned a quarterfinal spot opposite Serena Williams while Venus Williams will play Sharapova in the next round. Also Cibulkova takes on Li and Kvitova is to play Kerber.