Vinci defeated Polona Hercog 6-2, 7-6 (7-3) in 1 hour, 49 minutes. It was the only match of the day settled in two sets, and the shortest match by more than 40 minutes. The four second-round matches Thursday combined for about 9 1/2 hours of play.
Vinci finished with six breaks but needed to win the tiebreaker after she and Hercog traded a total of eight breaks in the second set.
Estrella Cabeza Candela ousted third-seeded Kristina Mladenovic 6-3, 2-6, 7-6 (8-6). She won just two more points (99-97) than Mladenovic in advancing to Friday's quarterfinals.
No. 5-seeded Lourdes Dominguez Lino took out Nastassja Burnett 7-5, 4-6, 6-3, fighting off 11 of 17 break points she faced.
Cabeza Candela draws the first match in Friday's quarterfinals, when she'll play Renata Voracova. Zakopalova takes on Dinah Pfizenmaier in a Court 2 battle. Dominguez Lino goes against Vinci back on Center Court ahead of Friday's finale pitting top-seeded and defending champion Sara Errani against Silvia Soler-Espinosa.
Swim Week Miami Beach 2014 [PHOTOS]