Wimbledon champion and Olympic gold medalist Serena Williams, seeded second in Cincinnati, logged a 6-3, 6-4 triumph over Greece's Eleni Daniilidou in a second-round match-up.
Venus Williams, a wild card in the event, took the first set of a first-round contest from the 12th-seeded Russian Maria Kirilenko 6-3, but Kirilenko rebounded to take the second set 7-6 (7-5). Williams then put her away with a 6-2 third set.
U.S. Open titlist and No. 3 Stosur got past Spain's Anabel Medina Garrigues 6-3, 6-7 (6-8), 6-4 in a second-round contest.
Fifth-seeded German Angelique Kerber got through to the third round with a 3-6, 6-1, 6-2 decision over Hungarian lucky-loser Timea Babos while Johanna Larsson of Sweden surprised eighth-seeded Marion Bartoli of France 6-4, 6-2.
Russian Ekaterina Makarova pulled off a first-round upset of 15th-seeded countrywoman Nadia Petrova 7-6 (10-8), 3-1, retired, and No. 17 Anastasia Pavlyuchenkova of Russia made the second round with a 6-4, 6-0 rout of Spaniard Carla Suarez Navarro 6-4, 6-0.
Yaroslava Shvedova, wild-card American Sloane Stephens, Czech Andrea Hlavackova, Kazakh qualifier Sesil Karatantcheva, Swede Sofia Arvidsson and Georgian lucky-loser Anna Tatishvili also notched first-round wins Tuesday.