Williams, who has won a career-best 27 consecutive matches, won the first seven games of a 6-0, 6-2 romp over 26th-seeded Sorana Cirstea in 61 minutes. The opening set took 23 minutes, with Williams winning 29 of the 42 points.
Cirstea did manage three break opportunities but Williams won them all while taking 70 percent of the points on serve. Williams has lost a total of six games over her six sets in the tournament.
Sharapova, the No. 2 seed, claimed a second-round win by finishing off a 6-2, 6-4 decision over Eugenie Bouchard. Sharapova was up 4-2 in the second set Thursday when play was called because of rain.
Fourth-seeded Agnieszka Radwanska, in Friday's final match, joined Sharapova in the fourth round with a 6-3, 6-4 win over Dinah Pfizenmaier. Radwanska dropped her serve only once and won about two-thirds of the points on serve.
Also winning third-round matches were No. 14 Ana Ivanovic, 15th-seeded Roberta Vinci and No. 21 Kirsten Flipkens. Unseeded players making the fourth round were Carla Suarez Navarro and Svetlana Kuznetsova while Kaia Kanepi claimed a three-set win in a second-round match.