Top seed Lindsay Davenport overcame Slovakian Daniela Hantuchova 6-2, 7-6 to reach the semi-finals of the New Haven Open in New Haven, Connecticut on Thursday.
The American cruised through the first set but had to fight hard in the second before snatching the tiebreak 7-5 to earn a meeting with unseeded Russian Anna Chakvetadze, who beat Jie Zheng of China 6-4, 6-4.
Davenport, who will regain the world number one ranking from Russian Maria Sharapova if she reaches the final, admitted she needed time to hit top form, having missed almost a month because of a back injury.
"I think it's about playing matches," Davenport said.
"I think it would be wrong of me to expect that I can come out after seven or eight weeks and be perfect.
"There's always going to be aspects of my game that need to be worked on and stuff that you can really only get from playing matches. And that's like hitting a good serve and getting ready for the ball to come back."
Fourth-seeded Russian Elena Dementieva suffered a surprise 6-4, 6-3 defeat by Anabel Medina Garrigues of Spain.
Medina Garrigues now plays second seed Amelie Mauresmo, after the Frenchwoman outplayed unseeded German Anna-Lena Groenefeld 6-3, 6-2.
In the men's event, American James Blake continued his resurgence with a 1-6, 6-3, 6-3 victory over sixth seed Tommy Haas of Germany.
Blake, who reached the final in Washington earlier this month, was blown off the court in the first set by Haas, the former world number two.
But Blake picked up his game in the second set and after levelling the match, he broke in the first and ninth games of the decider to clinch victory.
Blake now plays Juan Ignacio Chela after the Argentine followed up his victory over top seed Nikolay Davydenko with a 6-4, 6-1 win over Frenchman Fabrice Santoro.
Second seed Fernando Gonzalez of Chile lost 6-7, 7-5, 7-6 to Spaniard Fernando Verdasco but fourth seed Tommy Robredo of Spain crushed Austrian Stefan Koubek 6-2, 6-2 to reach the quarter-finals.
Third seed David Ferrer of Spain outgunned Thailand's Paradorn Srichaphan 6-4, 6-2, but seventh-seeded Chilean Nicolas Massu was upset 6-4, 6-4 by Romanian Victor Hanescu.
Fifth seed Feliciano Lopez of Spain and Russian Igor Andreev also advanced.
