Williams, No. 1 in the world and the tournament defending champion, beat seventh-seeded Sara Errani 7-5, 6-2 and second-ranked Sharapova followed with a 6-4, 6-3 decision over No. 16-seeded Ana Ivanovic.
Sharapova, who hasn't lost a set this week, finished off five of her six break opportunities and won half of the points when Ivanovic served. She was good on three-quarters of her first serves and, even with six double faults, won two-thirds of the points on serve. She also had six aces.
Williams has dropped one set in the tournament -- a 0-6 blip in the quarterfinals against Ana Medina Garrigues -- and was solid in improving to 5-0 lifetime versus Errani. She lost her serve twice in the first set but was more in control in putting the match away in the second.
Sunday's final will mark the second time this year and third time in their last four meetings that Williams and Sharapova will have played for a title. Williams was a three-set winner in the final in Miami in March. She is 12-2 all-time against Sharapova, having won the last 11 meetings. Sharapova hasn't beaten Williams since the 2004 WTA Tour Championships.