The big names were all tested in their second-round matches at the Family Circle Cup on Tuesday, including defending champion Andrea Petkovic.
Petkovic (seeded third), Angelique Kerber (fifth), Jelena Jankovic (sixth) and Caroline Garcia (eighth) were all taken to deciding sets, but progressed to the third round of the WTA Premier green clay tournament.
The 2014 champion saw off Chanelle Scheepers 1-6 6-1 6-2 despite starting slowly in Charleston, United States.
In her first clay-court match of the season, Petkovic was broken to 15 in three of her first four service games to concede the first set in limp fashion.
But Scheepers could not maintain her momentum, the South African getting broken herself thrice in each of sets two and three as Petkovic fought back to win in one hour, 50 minutes.
Petkovic's fellow German Kerber also started slowly, before earning a 3-6 6-3 6-4 victory over Evgeniya Rodina.
Jankovic blew a second-set match point on her own serve but avoided a shock as she defeated Tatjana Maria 6-3 6-7 (6-8) 6-1, while Garcia overcame Sachia Vickery 6-3 4-6 6-3.
In the day's other second-round affair, Lucie Hradecka defeated fellow qualifier Kristina Kucova 7-5 6-3 to advance to the last 16.
In round one results, ninth seed Sam Stosur and 12th seed Belinda Bencic were comfortable winners.
Stosur defeated Sesil Karatantcheva 6-2 6-4 to end the qualifier's tournament at the first main-draw hurdle, while Stosur's fellow Australian Casey Dellacqua bowed out - beaten 6-1 6-2 by Bencic.
There was less fortune for 10th seed Varvara Lepchenko and Anastasia Pavlyuchenkova, the 14th seed, with the pair retiring injured from their respective contests.
Lepchenko (back) called it quits when trailing Andreea Mitu 6-2 2-1, while Pavlyuchenkova (shoulder) shook hands with Sara Sorribes Tormo with the score at 6-4 3-0 in favour of the Spanish qualifier.
Sloane Stephens won an all-American battle with Bethanie Mattek-Sands 3-6 6-3 6-2, while 2014 finalist Jana Cepelova edged Elena Vesnina 6-2 6-7 (5-7) 7-6 (7-4).
Madison Brengle joined Stephens among the locals in the second round, with a 6-7 (2-7) 6-4 6-2 win over Edina Gallovits-Hall, while Lara Arruabarrena got past Cagla Buyukakcay 6-2 6-2.