Former world number one Ana Ivanovic fought from a set down to dump ninth seed Victoria Azarenka out of the Cincinnati Open on Monday night.
The 22-year-old Serbian triumphed 2-6 7-6 (8/6) 6-2 against the 21-year-old from Belarus and will take on Yaroslava Shvedova in the second round after the Kazakh's 7-5 6-4 victory over Russia's Alla Kudryavtseva.
Earlier, Vera Dushevina set up a second-round clash with top seed Jelena Jankovic by overcoming Anastasia Rodionova in straight sets.
The Russian won 6-2 7-6 (9/7) against the Australian qualifier to earn a date with Serbian Jankovic, who was given a first-round bye.
Dushevina's compatriot Dinara Safina will meet fourth seed Kim Clijsters in round two after getting past Italy's Roberta Vinci 7-5 6-4.
Fourteenth seed Aravane Rezai of France was the only seed other than Azarenka to fall on Monday, going down 4-6 6-3 6-4 to Serbian qualifier Bojana Jovanovski.
Elsewhere, Shahar Peer and Marion Bartoli advanced in straight sets.
Peer, the 13th seed from Israel, was 6-3 4-1 up when her Belarusian opponent Olga Govortsova retired due to heat illness, while 16th-seeded Frenchwoman Bartoli cruised past Spain's Anabel Medina Garrigues 6-4 6-0.
Ukraine's Alona Bondarenko and Spanish qualifier Nuria Llagostera Vives battled from a set down to beat Slovakia's Dominika Cibulkova and American qualifier Vania King respectively.
Uzbekistan's Akgul Amanmuradova thrashed Japanese veteran Kimiko Date Krumm 6-1 6-2, and there were also wins for Russia's Alisa Kleybanova, Italy's Sara Errani, Japan's Ayumi Morita and Romania's Monica Niculescu.