Nadia Petrova slumped to a 6-3, 6-3 defeat against Italy's Mara Santangelo in the second round of the Warsaw Cup on Wednesday.
There was victory though for American Venus Williams, who overcame Michaella Krajicek of the Netherlands 6-4, 6-3.
Third-seeded Russian Svetlana Kuznetsova withstood a strong early challenge from Ukrainian qualifier Kateryna Bondarenko to win 2-6, 6-2, 6-1 and sixth seed Anna Chakvetadze, also of Russia, overwhelmed Tathiana Garbin of Italy 6-2, 6-2.
Fifth-seeded Petrova, who had struggled to overcome unranked Polish junior Katarzyna Piter in her opening match, lacked consistency and was often hurried into errors by a resilient opponent.
The Russian hurled her racquet to the ground in frustration as she went through a disastrous patch in the opening set, dropping 10 of 11 points at one stage.
She began the second set well, conceding just three points in the first three games, but allowed Santangelo back into the match.
Claiming the next six games, the Italian clinched victory on her fourth match point when Petrova sent a forehand long.
Santangelo had managed to salvage just four games in her only previous meeting with Petrova, in Rome two years ago, but she is now a vastly improved player and a combination of solid serving and fine returns with some excellent running meant that Petrova was never able to enter a comfort zone.
"It was a great match. I'm very happy," said Santangelo, who earned her second victory over a top-10 opponent following a recent victory over Jelena Jankovic in Miami.
"I tried to do my best, be aggressive and play my game and try to wait for the points. It's a very important win for me. I've beaten another top-10 player and I want to keep going, I want to try to do my best, I want to go for it."
Williams had a solid match against Krajicek, who played with a sense of belief but was ultimately overpowered by an in-form opponent.
The unseeded American has already won more matches this season than in the whole of last year and she was never in difficulty against Krajicek.
After an early exchange of breaks, Williams broke again for the set when Krajicek hooked a forehand wide. Just one break decided the second set and that came at 3-2 when Krajicek made a backhand error.
"It was nice," Williams told reporters. "I was just glad it was a lot warmer. Yesterday I was prepared to play in the snow, so this was definitely an upgrade.
"I'm excited to be on the court every time that I'm out there. I feel like I have an opportunity and it's wonderful to be doing what I love."
