Doi topped No. 1-seeded Francesca Schiavone 7-5, 6-4. She lost all three of the break points she faced but managed to break Schiavone's serve five times. She took advantage of the second serve, winning 20-of-33 points in that situation.
Radwanska was a 6-3, 6-4 winner over second-seeded Sabine Lisicki. Lisicki was good on only 46 percent of her first serves and Radwanska capitalized, winning half of those points.
Czink edged by third-seeded Daniela Hantuchova 7-5, 7-6 (7-5) behind a 10-ace attack. Czink won nearly two-thirds of the points in her games serving.
Fourth-seeded Roberta Vinci was up 6-3 when Virginie Razzano retired and No. 5-seeded Jelena Jankovic advanced over Melanie South 6-1, 7-6 (7-3), but Andrea Hlavackova beat sixth-seeded Mona Barthel 7-6 (7-5), 6-2 and Elena Vesnina took out seventh-seeded Christina McHale 6-1, 1-6, 7-5.
Ekaterina Makarova, the No. 8 seed, topped Sesil Karatantcheva 7-6 (7-4), 6-3 and ninth-seeded Marina Erakovic got past Laura Robson 6-4, 3-6, 6-4.
Celebrity Families of 2014 [PHOTOS]