Lindsay Davenport continued the defence of her Filderstadt Grand Prix title with a 6-2, 3-6, 6-1 win over Anastasia Myskina in the quarter-finals on Friday.
She will play Daniela Hantuchova in the semi-finals after the Slovak defeated Italy's Flavia Pennetta 6-3, 6-4.
Top seed Davenport made a positive start, breaking Myskina in the opening game when the 2004 French Open champion netted a backhand.
With her groundstrokes doing their usual damage and her big serve keeping the Russian under pressure, Davenport broke again with an overhead to lead 4-1, and surrendered just four points on serve in the entire set.
But Myskina kept up with the rallies once the second set got underway, and broke to lead 3-1 on her fourth break point.
Davenport immediately broke back by forcing a backhand error from her return, but Myskina was able to take advantage of several careless errors from the American and broke again to lead 5-3 when Davenport double-faulted.
In the final set, Davenport reduced her errors and her aggressive groundstrokes again gave her the advantage. She swiftly built a 5-0 lead, failed to win a match point as Myskina finally held serve, and then comfortably served out for the match.
"It was definitely a match that went up and down in terms of level of play and concentration probably for both of us," said Davenport.
"I felt like I played better in the first set than the third set, but she started to give me a few errors again in the third and I don't feel she played as well on the bigger points in the final set."
Hantuchova was the steadier player against Pennetta, who had earlier upset fourth seed Justine Henin-Hardenne.
Pennetta played well in the rallies to keep herself in the match and Hantuchova had to fight off three break points as she served for the opening set.
The second set was decided by just one break, with Pennetta's fourth double-fault giving Hantuchova a 5-4 lead. The Slovak then served out the match to love, finishing with her sixth ace.