Andrea Hlavackova fell to Yaroslava Shvedova in the qualies, but they both ended up main draw winners.
Lucie Hradecka overpowered Urszula Radwanska, younger sister of Agnieszka Radwanska, in the first round.
Olga Govortsova raced through the first set but fell to Kateryna Bondarenko in the first round, 26 62 64.
Elena Vesnina, the 2011 finalist, battled almost two and a half hours to beat Stephanie Dubois, 76(10) 75.
Melanie Oudin qualified for the main draw but wound up falling to Anabel Medina Garrigues, 64 46 60.
Another American, Venus Williams, had little trouble in the first round, beating Iveta Benesova, 64 63.
Young Italian Camila Giorgi came from the qualies but fell first round to Barbora Zahlavova Strycova, 61 63.
No.11 seed Christina McHale was the biggest upset of the first round, losing to Aleksandra Wozniak, 75 57 64.
Marion Bartoli won a three-hour-plus marathon to beat Vera Dushevina in her opening match, 62 67(3) 64.
Sam Stosur had trouble closing the second set out, letting 5-2 become 5-all, but beat Jamie Hampton, 60 75.
Two-time finalist Vera Zvonareva cruised through her opening match against Kateryna Bondarenko, 61 61.
Serena Williams was all business in her second round match against last year's finalist here, Elena Vesnina.
Serena Williams blasted 11 aces to just three double faults to win her opener against Elena Vesnina, 63 64.
Sabine Lisicki battled past lucky loser Andrea Hlavackova in a center court three-setter, 26 63 64.
Eleni Daniilidou got a little help as she missed a 63 31 lead and lost out to Anastasia Pavlyuchenkova.
Anastasia Pavlyuchenkova tightened the screws and outdid former Top 15 player Eleni Daniilidou, 36 64 64.
Sam Stosur was one of five Family Circle Cup champions to reach the round of 16 in Charleston this year.
Jelena Jankovic had beaten Venus Williams four times in a row on clay, but Williams won this time, 75 60.
Yaroslava Shvedova served up a run to the third round as a qualifier, but she was stopped by Sabine Lisicki.
Polona Hercog got her first Top 10 win in the third round on Thursday, beating World No.7 Marion Bartoli.