Third seed Elena Dementieva, who collapsed with cramp while serving for the match, recovered to defeat Slovenia's Katarina Srebotnik 4-6, 7-5, 7-5 in the second round of the Stuttgart Grand Prix on Wednesday.
Svetlana Kuznetsova, the second seed, joined fellow Russian Dementieva in the quarter-finals when she swept aside German wildcard Martina Muller 6-1, 6-4.
Having broken Srebotnik to lead 5-4 in the deciding set, Dementieva fell to the floor in pain.
After several minutes of treatment and a sympathetic hand on the shoulder from Srebotnik, the Russian carried on playing and had her serve broken.
But she dug deep to pound a succession of powerful groundstrokes to break serve again before completing one of the most difficult wins of her career.
"I didn't want to give up and I put in so much, everything that I had today," Dementieva told Reuters.
"When the cramping happened I was in shock, I didn't want to quit. I wanted to continue because I was almost closing the match.
"It was a very difficult moment. I was thinking that if I won one more game I'm going to have a day off and that was really going to help me recover. I didn't want to lose and wanted to fight, fight."
Dementieva welcomed the announcement that U.S. Open champion Maria Sharapova wanted to join Russia's Fed Cup campaign next season.
Russia have been drawn at home against Spain in the first round in April.
"If she (Sharapova) plays it's going to be very helpful for the team," said Dementieva. "She's a very strong player and we have a lot of chances to win if she's playing."
Anastasia Myskina once said she would refuse to play if Sharapova's father Yuri was present.
But Dementieva dismissed the idea of unrest in the Russian camp.
"I don't see any problems with her father," said Dementieva.
"He's an emotional guy but it is nothing to do with his daughter. Maria is a nice girl and I don't see any problems."
In first-round matches played on Wednesday, eighth-seeded Serb Jelena Jankovic defeated Frenchwoman Mary Pierce 7-6, 6-3 and unseeded Slovak Daniela Hantuchova ousted Austrian Sybille Bammer 6-3, 5-7, 6-3 to earn a meeting with Russian Dinara Safina.