Ashleigh Barty has fought back from a set down to win her second round match at the WTA clay-court tournament in South Carolina but Daria Gavrilova is out after a three-set loss.
Ninth-seeded Australian Barty dropped the first set to unseeded German Tatjana Maria before powering to a 4-6 6-3 6-2 victory.
Her round of 16 opponent is Latvian eighth seed Anastasija Sevastova, who beat qualifier Caroline Dolehide in three sets.
Barty's countrywoman Gavrilova, the 11th seed, bounced back after losing the first set to Italy's Camila Giorgi and looked to turn the tide but unforced errors resurfaced as she was beaten 6-2 2-6 6-3.
Five double faults in the opening set from Gavrilova set the tone, three of them coming in her first two service games. She saved four break points before surrendering the set.
A reverse in the second appeared to give the world No.24 the momentum but Gavrilova's troubles returned in the deciding set.
A tight eighth game saw Giorgi get the break and she made no mistake with her first match point.
Meanwhile, world No.77 Kristyna Pliskova rallied from a set down to knock out two-time Wimbledon champion and Petra Kvitova.
Czech second seed Kvitova won six of the first seven games to take the opening set before countrywoman Pliskova came back for a 1-6 6-1 6-3 win.
Sixth-seeded Briton Johanna Konta suffered a shock straight-sets defeat to world No.219 Fanny Stollar.
Konta, who received a bye in the first round, was soundly beaten 6-3 6-4 by the 19-year-old Hungarian qualifier.
A host of other seeds progressed with American Madison Keys, Germany's Julia Georges, Naomi Osaka of Japan, Dutchwoman Kiki Bertens, Irina-Camelia Begu of Romania, Frenchwoman Alize Cornet and Elena Vesnina of Russia reaching the last 16.
Unseeded winners were American Bernarda Pera and Italian wildcard Sara Errani.
