Third seed Svetlana Kuznetsova came from a set down to defeat Venus Williams in the quarter-finals of the J&S Cup in Warsaw.
Kuznetsova is trying to win her first title of 2007
The Russian won 3-6 6-3 6-4 and goes on to face Alona Bondarenko, who led 6-2 3-1 when Julia Vakulenko retired.
"I really didn't feel like I played that well," said Williams. "Just so many errors, you know, I gave away so many free points, it's too much."
Justine Henin made the last four with a 6-2 6-1 win over Mara Santangelo.
"Today was almost perfect," said the Belgian. "It was a good match. I'm very happy the way I played, very consistently and very focused on every point."
Fourth seed Jelena Jankovic progressed after Anna Chakvetadze retired with a shoulder injury when trailing 7-6 (7-1) 3-1.
"I thought she had something wrong in the tie-break," said Jankovic.
"We were both on the same level and all of a sudden she kind of gave up and she wasn't the same player."