Clay court specialist Anabel Medina Garrigues battled past qualifier Melanie Oudin 6-4 4-6 6-0 in the first round of the WTA Family Circle Cup in Charleston.
The Spanish 10th seed will face Anastasia Rodionova next, after the Australian beat qualifier Melanie Czink 6-2 2-6 6-1.
Medina Garrigues has won 10 WTA titles on clay - more than any other active player - but had to grind it out over the first two sets before coming through in two hours and 29 minutes.
Unseeded Canadian Aleksandra Wozniak outlasted American 11th seed Christina McHale 7-5 5-7 6-4 in a two-hour, 48-minute marathon.
Wozniak, a former world number 21, had three aces and won 70 per cent of her first-serve points.
In other matches on Monday, Argentinian Paula Ormaechea surprised 15th seed Chanelle Scheepers 6-1 1-6 6-4 while 16th seed Jarmila Gajdosova lost to Swiss qualifier Stefanie Voegele 6-4 2-6 6-4.
Serena Williams begins her challenge on Tuesday against Elena Vesnina of Russia, who beat Canada's Stephanie Dubois 7-6 (12/10) 7-5.
