Jessica Pegula of the United States celebrates match point against Yulia Putintseva of Kazakhstan during the Credit One Charleston Open at Credit One Stadium. AFP
Pegula, the world number five from the United States, had clawed back a set but was broken to trail 0-2 in the third before mounting a final fightback.
"All I just kept thinking was, like, welcome to the clay court season," Pegula said after grinding out the win on Charleston's green clay.
Pegula, who enjoyed a first-round bye, said the breezy conditions and challenging shadows made it hard to respond aggressively to the high, looping shots from 72nd-ranked Putintseva of Kazakhstan.
"She's a really tricky opponent in general," Pegula said.
"I feel like especially on clay she can be really crafty, use high balls, low balls, slices, drop shots, and I felt like she was just honestly toying with me there for quite a while," added the American, who was broken as she served for the match at 5-4 but broke back to give herself another opportunity to close it out.
Pegula is chasing her second title of the year, after a victory in Dubai in February.
Second-seeded Ekaterina Alexandrova withdrew from the tournament before her second-round opener on Wednesday, saying she had "a bit of an injury" picked up in Miami.
The 13th-ranked Russian was replaced in the draw by Ekaterine Gorgodze of Georgia.
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