Vera Zvonareva and Patty Schnyder were both first-round casualties on a day of surprises in the Istanbul Cup on Tuesday.

Zvonareva, the world number seven, failed to make the most of a convincing second set and was beaten 6-2 1-6 6-4 by Ukrainian Mariya Koryttseva.

And Schnyder was the latest casualty of Paraguay's in-form Rossana De Los Rios, a quarter-finalist in both Zagreb and Portoroz, who triumphed 7-6 (7/3) 2-6 6-3.

Fourth seed Stefanie Voegele was another casualty, beaten 6-2 7-6 (7/4) by unseeded Pole Urszula Radwanska.

But it proved much more straight-forward for third seed Anabel Medina Garrigues as the Spaniard posted a 6-4 6-2 win over Belarus qualifier Anastasiya Yakimova.

Fifth seed Vera Dushevina was another winner over qualifier Yuliana Fedak, while eighth-seeded Lucie Hradecka also advanced.