CHARLESTON, S.C. — Top-seeded American Sloane Stephens outlasted Spain's Sara Sorribes Tormo 7-6 (4), 7-6 (4) to advance Tuesday at the WTA's Volvo Car Open.

Stephens, the 2017 U.S. 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 Mahaela Buzarnescu of Romania, No. 15 Maria Sakkari of Greece and No. 16 Petra Martic of Croatia.

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