Justine Henin-Hardenne saved two match points on Monday before outgunning Russia's Svetlana Kuznetsova 7-6 4-6 7-5 to reach the quarter-finals.
The Belgian, champion here in 2003, hung on in the third set against the U.S. Open champion, clinching victory in three hours 15 minutes to set up a clash with second seed and Wimbledon champion Maria Sharapova.
The Wimbledon champion needed just three games to close out her match that was suspended due to rain on Sunday.
"I felt she was nervous when she had the match points, I could see she was afraid to win the match and when you see that in the eyes of your opponent it makes you feel very good," said the Henin-Hardenne.
"After the match points I understood that I could win the match and I kept fighting." The former world number one has now won 21 consecutive matches including titles in Warsaw and Berlin.
She scraped through the opening set tiebreak after Kuznetsova had wasted a set point.
Kuznetsova used her powerful forehand to dominate the second set, breaking serve three times, and the Russian seemed on course for her first quarter-final at Roland Garros when she led 5-3 in the decider.
Twice she reached match point on the Henin-Hardenne serve and twice she failed to close out the match, narrowly missing an attempted backhand winner down the line on the first.
Henin-Hardenne took advantage of sloppy play to break back when Kuznetsova served for the match and the former world number one showed all her experience as Kuznetsova crumbled.
"I didn't play my best game today, but I was mentally very strong," said Henin-Hardenne, who missed the start of the year after suffering a bad knee injury last December.
Henin-Hardenne said she is now ready for an even tougher challenge against Sharapova on Tuesday.
"Kuznetsova hits the ball very heavy but Sharapova plays even quicker," she said. "But I believe I can win."
Kuznetsova was left to ponder losing for the second year running at Roland Garros having held match points.
Last year she failed to finish off eventual champion Anastasia Myskina at the same stage.
"I feel like the match was in my hands, I had so many chances," said the Russian after her seventh defeat in eight meetings with Henin-Hardenne.
"I lost it, she didn't win it. I was dictating the points and I felt much fitter than her. But I guess her experience showed in the end."
Resuming on 6-2, 3-3 against Spain's Nuria Llagostera Vives on a windswept Court Suzanne Lenglen, Sharapova reeled off the three games required to advance 6-2 6-3.
"I guess it was good just to have a good night's sleep," the 18-year-old said.
"I think I've been playing a lot better in my last two rounds than I did in my first two," Sharapova said.
"I've actually been feeling a lot better. I know it's definitely going to be a tough match either way. You have to expect the best.
"You know, hopefully I'll go out and just be even tougher and play even better than I have. That's the only way to go."
The powerful baseliner knows that whoever she meets is going to try to grind her down on the slow Roland Garros clay.
"It's going to depend on the conditions," she said. "If the conditions are going to be heavier, a lot of the points are going to be long.
"I feel fit enough to be able to do that. It's just a matter of mentally going out there and doing it.
"I think I'm getting better and better. I've said this before... If people underestimate me on clay then they'll be surprised," she grinned.
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