Charleston - Top-seeded American Sloane Stephens outlasted Spain's Sara Sorribes Tormo 7-6 (7/4), 7-6 (7/4) to advance on Tuesday at the WTA's Volvo Car Open.
Stephens, the 2017 US Open champion, needed almost 2 hours, 40 minutes to put away Tormo in the season's first clay-court tournament.
The 2016 Volvo Car Open champion was not crisp during several stretches.
She fell behind Sorribes Tormo 5-2 in the first set before rallying. Stephens also squandered two match points at 5-4 in the second set before winning the tiebreaker.
Defending champion Kiki Bertens of the Netherlands, the second seed, defeated Martina Trevisan of Italy 6-2, 6-1 to move into the third round.
Bertens was sharp in winning, needing less than an hour to dispatch Trevisan.
The start of play was delayed three hours because of rain.
Other seeded players advancing were No 11 Danielle Collins of the United States, No 12 Mihaela Buzarnescu of Romania, No 15 Maria Sakkari of Greece and No 16 Petra Martic of Croatia.
Results on Tuesday in the WTA tournament in Charleston, South Carolina (x denotes seed):
Sloane Stephens (USA x1) bt Sara Sorribes (ESP) 7-6 (7/4), 7-6 (7/4)
Kiki Bertens (NED x2) bt Martina Trevisan (ITA) 6-2, 6-1
Kateryna Kozlova (UKR) bt Kristyna Pliskova (CZE) 7-5, 6-4
Danielle Collins (USA x11) bt Madison Brengle (USA) 6-1, 6-3
Kaia Kanepi (EST) bt Veronika Kudermetova (RUS) 7-6 (7/4), 6-3
Petra Martic (CRO x16) bt Amanda Anisimova (USA) 6-4, 2-6, 6-1
Laura Siegemund (GER) bt Emma Navarro (USA) 7-5, 6-4
Lauren Davis (USA) bt Ysaline Bonaventure (BEL) 6-4, 0-6, 6-2
Mihaela Buzarnescu (ROM x12) bt Magdalena Frech (POL) 6-1, 4-6, 7-5
Maria Sakkari (GRE x15) bt Conny Perrin (SUI) 7-5, 3-6, 6-1
Andrea Petkovic (GER) bt Varvara Lepchenko (USA) 6-0, 6-4