Second seed Venus Williams needed three sets to beat battling Indian Sania Mirza 6-1 3-6 6-2 in the second round of the Family Circle Cup on Wednesday.
After dominating the opening set, American Williams found herself in trouble in the second with the 100th-ranked Indian producing some great defence to save 10 out of 11 break points while breaking the American twice.
Williams finally took control of the match in the third set, dominating Mirza to finally move on after a battle lasting almost two hours.
Williams will face Sabine Lisicki, seeded 16th, in Thursday's third round match after the German beat Slovakia's Lenka Wienerova 6-4 6-3.
"These kind of matches are great to pull out," Williams told reporters. "I've been in these situations before, so I rely on that."
American Melanie Oudin also advanced to the third round with an upset 7-5 6-0 victory over No 29 Aleksandra Wozniak of Canada, the ninth seed.
"I was really happy with the way I played and how I kept it up, especially through playing a set and not letting her come back at all," said Oudin, ranked No 176 in the world.
Fifth-seed Caroline Wozniacki of Denmark continued her progress with a 6-3 6-3 win over Russian Alla Kudryavtseva but number eight seed Patty Schnyder of Switzerland was eliminated by Russia's Elena Vesnina 2-6 7-6 5-7.
China's Peng Shuai advanced, but only just, with a 7-5 2-6 7-5 victory over Akgul Amanmuradova of Uzbekistan.
There was a surprise in the all-Ukrainian clash between 11th seed Alona Bondarenko and lower ranked Viktoriya Kutuzova, who ran out the 6-4 7-5 winner.
Russian Anastasia Rodionova beat American 12th seed Bethanie Mattek-Sands 6-2 6-4 to go through to the third round.