Heat was again at issue with temperatures in the upper 90s degrees Fahrenheit through Wednesday's play. Temperatures of more than 100 degrees contributed to an illness that led to top-seeded Ksenia Pervak retiring from a match Tuesday.
Panova saved 9-of-11 break points en route to a 4-6, 76- (8-6), 6-3 win over Sandra Zaniewska. She fought off five break chances in the third set while getting two of her three breaks of the day in the set.
No. 3-seeded Mandy Minella beat Marta Domachowska 6-4, 7-5. She also faced a series of break points but lost her serve just once despite nine break-point chances for Domachowska.
Fifth-seeded Bojana Jovanovski, despite dropping serve three times, defeated Valeria Solovieva and No. 6-seeded Nina Bratchikova advanced when Estrella Cabeza Candela retired prior to the second set. Bratchikova won the first set 6-0.
Magdalena Rybarikova rolled past Tamarine Tanasugarn 6-1, 6-0 in 48 minutes. Rybarikova took 71 percent of the points overall and 24-of-30 on serve.
Also Wednesday, Julia Cohen topped Alla Kudryavtseva 6-1, 6-4; Olga Puchkova got by Alberta Brianti 3-6, 7-6 (7-2), 6-1; and Aleksandra Krunic topped Laura Pous-Tio 7-6 (7-5), 6-3.
The quarterfinal pairings have Cohen playing Rybarikova and Puchkova meeting (Minella) in the top of the draw. The other matches pit Panova versus Bratchikova and Jovanovski against Krunic.