The 31-year-old Czech cruised past Spaniard Silvia Soler-Espinosa 6-4, 6-1, and now goes on to meet Poland's Katarzyna Piter, who battled past German Dinah Pfizenmaier 5-7, 6-3, 6-1 on Day 3 at Jockey Club Brasileiro.
Also gaining the quarterfinals was third-seeded Argentine Paula Ormaechea, who bested Kiki Bertens of the Netherlands 7-5, 7-5.
Her next opponent will be Italian Nastassja Burnett, who rallied to defeat Belgian qualifier Alison Van Uytvanck 0-6, 6-3, 6-2.
Fifth-seeded Japanese Kurumi Nara took a first-round victory Wednesday, dispatching Su-Wei Hsieh of Taiwan 6-3, 6-2.
German Anna-Lena Friedsam moved on the second round as well, routing Ukrainian Nadiya Kichenok 6-2, 6-3.
2014: NFL Cheerleaders [PHOTOS]
Michael Sam cut from the Dallas Cowboys