Pervak was bounced 7-6 (7-3), 6-2 by Italian Alberta Brianti, while Hradecka fell 3-6, 6-4, 7-6 (7-3) to Ukraine's Lesia Tsurenko at The Racquet Club of Memphis.
Another seeded player was also eliminated in Wednesday's action when Sweden's Sofia Arvidsson prevailed over No. 5 Pauline Parmentier of France, 7-6 (7-5), 0-6, 6-3.
Arvidsson, who the Memphis event in 2006, now enters the quarterfinals where she'll face Tsurenko.
Also gaining the round of eight was France's Stephanie Foretz Gacon, who bested Italian qualifier Camila Giorgi 7-5, 6-4, and now will match up against Russian Vera Dushevina.