Serena Williams recorded a second-round victory Tuesday, while Venus Williams posted a first-round win at the WTA's $2.168 million Western & Southern Open.
Serena, the No. 2 seed, defeated Greek Eleni Daniilidou 6-3, 6-4.
The Wimbledon and Olympic gold medal champion Serena fired nine aces past Daniilidou to secure her spot in the third round.
U.S. Open titlist Sam Stosur, the third seed, outlasted Anabel Medina Garrigues of Spain 6-3, 6-7 (6-8), 6-4.
In some other second-round play, fifth-seeded German left-hander Angelique Kerber overcame Hungarian lucky-loser Timea Babos 3-6, 6-1, 6-2 and Johanna Larsson of Sweden upset eighth-seeded Frenchwoman Marion Bartoli 6-4, 6-2. Kerber was a Wimbledon semifinalist last month.
The former world No. 1 Venus, a wild card this week, upended 12th-seeded Olympic semifinalist Maria Kirilenko of Russia 6-3, 6-7 (5-7), 6-2 on the hardcourts at the Lindner Family Tennis Center.
Another opening-round upset came when Ekaterina Makarova got past 15th-seeded fellow Russian Nadia Petrova 7-6 (10-8), 3-1, retired, while 17th-seeded Russian Anastasia Pavlyuchenkova avoided a first-round upset by cruising past Spaniard Carla Suarez Navarro 6-4, 6-0.
Yaroslava Shvedova took down Lucie Safarova, the No. 16 seed, by a 6-3, 6-4 margin.
In additional opening-round action involving Americans, wild card Sloane Stephens handled Bulgarian Tsvetana Pironkova 6-4, 6-1, while Italian Roberta Vinci drubbed Madison Keys 6-3, 6-3 and Czech Andrea Hlavackova dismissed fellow qualifier Bethanie Mattek-Sands 6-3, 7-5.
Chanelle Scheepers of South Africa was leading Christina McHale 3-6, 6-3, 3-0 when the American retired from the match.
Additional first-round wins came for Slovak Daniela Hantuchova, Romanian Sorana Cirstea, Kazakhstanian qualifier Sesil Karatantcheva, Swede Sofia Arvidsson, and Georgian lucky-loser Anna Tatishvili.