Williams, No. 1 in the world, routed 14th-seeded Dominika Cibulkova 6-0, 6-1 in 66 minutes. Williams fired 12 aces and saw just two break points.
Williams won 67 percent of the points on serve and 66 percent off Cibulkova's serve.
It was the 21st consecutive match win for Williams, which matches her career best. It is the third time she's won 21 in a row, with the other streaks coming in 2002 and 2003.
Sharapova, the two-time defending champion, claimed a 6-2, 6-1 win over 16th-seeded Sloane Stephens. Sharapova had seven double faults but still won more than 60 percent of the points when serving and saved three of the four break points Stephens had.
Seventh-seeded Sara Errani moved into the quarterfinals when 12th-seeded Maria Kirilenko, down 6-3, 2-0, retired with a knee injury. Ninth-seeded Samantha Stosur posted a small upset by beating No. 8-seeded Petra Kvitova 7-5, 2-6, 6-1.
Williams will next take on Suarez Navarro while Jankovic plays Halep. Sharapova meets Errani and Azarenka goes against Stosur in the other quarterfinals Friday.