Holder Justine Henin-Hardenne advanced to the German Open semi-finals with a 6-4, 7-6 victory over Russian Svetlana Kuznetsova in Berlin on Friday.
The French Open champion must wait to discover her opponent after bad light ended play in the match between world number one Amelie Mauresmo and 1999 winner Martina Hingis with the pair level at one set apiece.
Mauresmo started strongly, winning the first two games, but unseeded Swiss Hingis fought back to take the first set 6-4.
The Frenchwoman, who lifted the title in 2001 and 2004, then hit back by taking the second 6-4. The final set will be played on Saturday.
Third seed Henin-Hardenne's probing groundstrokes and booming backhand proved too much for 2004 US Open champion Kuznetsova under blue skies at the Steffi Graf Stadium.
"It was a tough one, it was a great fight," the Belgian told reporters. "I didn't give it away in the tie break which I played very aggressively."
Henin-Hardenne said she would have to play her best on Saturday, whoever she faced.
SCHNYDER OUT
"I have to take my hat off to Hingis for what I have seen here and Amelie is the best in the world, she has proven that to everyone," she said.
The surprise of the day came when unseeded Chinese Na Li defeated Switzerland's Patty Schnyder 2-6, 7-6, 7-6 after saving three match points in the second set.
Fourth seed Schnyder went down even though the 24-year-old Na struggled with a thigh injury and foot problem.
"Compared with the last two matches I had a much calmer and more positive attitude," said Na, who next meets second seed Nadia Petrova.
Petrova put out fellow Russian Dinara Safina 3-6, 6-4, 6-3.
Last year's runner-up Petrova, ranked fourth in the world, said: "Everything seemed to work in her favour, she hit the lines and really pushed me back but no one can keep on playing tennis like that for long.
"You don't like to lose to anyone but definitely even less against a fellow Russian."
