Williams, coming off her triumph at Wimbledon last weekend, recorded a 6-4, 6-0 quarterfinal victory over Chanelle Scheepers.
Sorana Cirstea will face Williams in the semifinals after defeating Dominika Cibulkova 6-7 (5-7), 6-2, 6-0.
Vandeweghe reached her milestone by defeating Urszula Radwanska 6-4, 6-4.
Vandeweghe's semifinal opponent will be Yanina Wickmayer, who eliminated second-seeded Marion Bartoli 6-3, 6-2.
Swim Week Miami Beach 2014 [PHOTOS]