ISTANBUL, Turkey - It didn't take long for the upset bug to bite at the Istanbul Cup, as the No.1 and No.2 seeds, who have 20 Sony Ericsson WTA Tour singles titles between them, were eliminated on Day 2 of the event.

Top seed Vera Zvonareva, playing for the first time since withdrawing from the third round of Wimbledon due to a right ankle injury, fell victim to Mariya Koryttseva, 62 16 64. Koryttseva's win over the world No.7 was her first Top 10 win; in fact she had never beaten anyone ranked higher than No.30 previously.

"It's very difficult to come back after injury. I had a very experienced opponent out there today and I knew I had to come up with a better game than her. I tried my best, fought until the end and saved a couple of match points, but I wasn't able to win," Zvonareva said. "Even though I didn't do as well as I wanted to here, I really enjoyed my time in Istanbul. I'm very impressed with the city and the tournament and I hope I'll be back."

Tuesday's other stunner was 33-year-old Rossana de los Ríos upending fellow veteran and No.2 seed Patty Schnyder, 76(3) 26 63. It was de los Ríos' first win against the 30-year-old Schnyder in four career match-ups, though they hadn't played since 2002. Next up for the Paraguayan is the red-hot Andrea Petkovic, who is riding a six-match winning streak after capturing her first Tour singles title last week at Bad Gastein and winning her first round match here over Sandra Zahlavova on Tuesday.

The three other seeds in action steered clear of upsets, as third-seeded Anabel Medina Garrigues raised her career record against qualifier Anastasiya Yakimova to 4-0 with a victory, fifth-seeded Vera Dushevina topped qualifier Yuliana Fedak and eighth-seeded Lucia Hradecka got past Turkish wildcard Cagla Buyukakcay. No.6 seed Yaroslava Shvedova withdrew from the tournament with a right arm injury.

Also advancing Tuesday were Urszula Radwanska, Julia Goerges, Angelique Kerber and qualifier Ekaterina Dzehalevich.