Williams has been trying to climb her way into the world's top 16 before the French Open, which begins on May 27, having dropped as low as 71 after wrist and knee injuries.
Top seed and former Wimbledon champion Maria Sharapova beat Bulgarian Tsvetana Pironkova 6-4, 7-6.
Third-seeded Patty Schnyder of Switzerland beat Taiwanese Chan Yung-Jan 6-1, 6-1, while American Vania King defeated Turkish Ipek Senoglu 6-3, 7-5.
Ekaterina Dzehalevich of Belarus beat Georgian Anna Tatishvili 6-3, 7-5.
