Wednesday's matches set the pairing for the second semifinal. Li Na was to meet Caroline Wozniacki after Agnieszka Radwanska and Dominika Cibulkova played.
Williams is the world's top-ranked player, defending tournament champion and a six-time winner. She was in top form while defeating Germany's Angelique Kerber 6-2, 6-2.
Williams served seven aces and faced one break point as she crushed Kerber in 63 minutes.
Sharapova, runner-up the past three years and five times in total, comfortably beat Czech eighth seed Petra Kvitova 7-5, 6-1.
MORE: Sharapova-Kvitova video
Sharapova has a dreadful record against Williams, who has won their past 14 matches and holds a 15-2 head-to-head.
"When you're playing champions, you like to play your best," Williams said. Sharapova "always gives me her best. ... I love playing her. I really do. It doesn't matter what surface. She's one of my favorite people to play."
Sharapova believes she is up for the test.
"It's no secret that she's been a big challenge of mine, an opponent that obviously I would love to beat," Sharapova said.
"There are certainly ways I need to step up in certain situations I haven't been able to do in the past against her, but it's great I have the opportunity to play her again."
