World number one Dinara Safina overcame a gutsy fightback from Lucie Safarova to beat the unseeded Czech 6-0, 4-6, 6-3 and seal a place in the last eight of the Madrid Open on Thursday.
The Russian raced through the first set but stumbled in the second to twice lose her serve before slipping 2-0 behind in the third.
She rallied to break back twice and wrapped up the win when Safarova sent a return over the baseline on the second match point.
Top seed Safina will play Alona Bondarenko on Friday for a place in the last four after the Ukrainian beat Russian Anna Chakvetadze 6-0, 2-6, 6-3 earlier in the day.
"I started very well, very aggressive, but then I just stopped and let her back in," Safina told a news conference.
"All I can take from the match is how I played in the first set, which is how I should play all the time. I hope I play two sets like that in my next match."
Fourth seed Jelena Jankovic swept into the last eight with a 6-2, 6-2 victory over qualifier Elena Vesnina, another Russian.
The Serbian former world number one had a slow start to the season when she struggled with her fitness and the distraction of her mother's ill health, but seems to have regained her focus ahead of the French Open which starts later this month.
Jankovic stuttered when serving for the match at 5-1 in the second set but broke Vesnina for the sixth time in the next game when the Russian failed to deal with a thumping backhand.
Swiss Patty Schnyder is Jankovic's opponent on Friday for a place in the semi-finals.
Frenchwoman Amelie Mauresmo and Russian qualifier Vera Dushevina booked their places in the last eight on Wednesday.
Former number one Mauresmo meets Hungarian Agnes Szavay on Friday and Dushevina will play Caroline Wozniacki of Denmark.