Williams, in her first match since her career-best 34-match winning streak was broken in the fourth round at Wimbledon, defeated Sesil Karatantcheva 6-1, 6-2 in 64 minutes. Williams was good on just half of her first serves and faced five breaks points -- winning four.
However, she took 55 percent of the points when receiving serve and finished off five of her eight break chances.
Qualifier Andrea Gamiz stunned fourth-seeded Tsvetana Pironkova 6-1, 6-3 with five breaks. Gamiz also won more than half (31-of-60) of the points when Pironkova served and lost her serve once in the match.
No. 3-seeded Klara Zakopalova needed just 48 minutes to dispatch Ellen Allgurin 6-1, 6-1. Both the games she lost came on breaks but she finished off 7-of-10 of her own break chances.
Sixth-seeded Lesia Tsurenko topped Anastasia Grymalska 6-3, 5-7, 6-1.
Also Tuesday, Anna Tatishvili beat Belinda Bencic 2-6, 6-4, 6-4; Teliana Pereira defeated Dinah Pfizenmaier 3-6, 6-2, 7-5; Richel Hogenkamp got by Lara Arruabarrena 6-3, 6-3; Nina Bratchikova advanced over Lesley Kerkhove 6-3, 6-1; Mathilde Johansson took a 6-2, 6-3 decision from Julia Cohen; and Alexandra Dulgheru beat Caroline Garcia 7-6 (7-2), 6-1.