Errani defeated qualifier Melina Czink 6-4, 1-6, 6-1. Errani took two-thirds of the points in the decisive third set. She was particularly strong when serving, dropping just five points in four games.
Barbora Zahlavova Strycova claimed an upset win, beating fourth-seeded Klara Zakopalova 6-3, 6-3 on the strength of four service breaks.
Elena Vesnina eliminated Pervak with a 6-2, 6-3 decision. Vesnina lost her serve once but still won 69 percent of the points on serve. She had five breaks in the win.
Sixth-seeded Petra Martic advanced with a 6-4, 6-1 win over Hsieh Su-Wei and No. 5-seeded Marina Erakovic moved on when, after Erakovic won the first set 6-0, Akgul Amanmuradova retired.
Also Wednesday, Alberta Brianti defeated Lesia Tsurenko 5-7, 7-5, 6-4 in a 3-hour match; Anna Tatishvili routed Vanda Lukacs 6-1, 6-2 in a 54-minute match; and Aleksandra Wozniak recorded a 6-7 (2-7), 6-0, 6-0 win over Alexandra Cadantu.
Errani goes against Brianti and Wozniak meets Tatishvili in the quarterfinals from the top half of the draw. Erakovic plays Zahlavova Strycova and Martic faces Vesnina in the other quarterfinals.