Serena Williams, seeded ninth, is 17-0 on clay courts this year after she moved into the semifinals. She was up 4-0 in the first set when Flavia Pennetta retired due to a right wrist injury.
Sharapova, the world No. 2, defeated Venus Williams 6-4, 6-3, winning nearly two-thirds of the points on serve. She was able to finish off four of her nine break-point chances.
Her semifinal opponent Saturday will be 12th-seeded Angelique Kerber, who ousted fourth-seeded Petra Kvitova 7-6 (7-2), 1-6, 6-1. Each player had five breaks but two of Kerber's came in the third set when she didn't face a break point.
No. 8-seeded Li Na claimed a 6-1, 7-6 (7-4) decision over 14th-seeded Dominika Cibulkova. Li won 55 percent of points off Cibulkova's first serve and wound up with five breaks.
She will go against Serena Williams in the semifinals. Williams is 5-1 lifetime against Li, including having won the last four meetings. Sharapova and Kerber have split their two previous meetings, both of which were this year.