Paris ? Andre Agassi was in a rut: His rhythm was off, his much younger opponent couldn’t miss, his deficit was growing.

And this is what ran through his mind: “It can’t get any worse.”

Down two sets and a break in the third, Agassi called on every shred of savvy to come back again and again until he finally overcame wild-card entry Paul-Henri Mathieu 4-6, 3-6, 6-3, 6-3, 6-3 Monday to reach the French Open quarterfinals.

With top-seeded Lleyton Hewitt and three-time champion Gustavo Kuerten gone, Agassi is looking increasingly like the favorite, thanks largely to his resolve.

“The great part about tennis is you can’t run out the clock. You can’t just get a lead for yourself and slow down,” said Agassi, at 32 a dozen years older than Mathieu. “As long as we were still playing, I had a chance.”

Barely, though. He could have folded at various junctures.

Take your pick: trailing 2-0 in the third set; when consecutive double faults set up Mathieu’s break in the third game of the final set; two games later, when Agassi faced two break points that could have put him down 4-1.

Each time, somehow, the oldest man left in the tournament came through with an ace (he finished with 11), or with a groundstroke hit at an angle a billiards player would appreciate, or with one of eight delicate drop shots.

“When he wants to win a specific point, he wins it,” said the 107th-ranked Mathieu, who stunned No. 14 Jiri Novak and No. 23 Fabrice Santoro last week. “He’s lived the situation 200 times already. For me it was the first time. That’s the difference.”

How great is the gulf? Mathieu, who won the 2000 junior title at Roland Garros, has eight career tour-level match victories 705 fewer than Agassi.

Yet it was the Frenchman who dominated early, placing shots by the lines and celebrating by pounding his chest with his fist.

Andre Agassi, left, shakes hands with France's Paul-Henri Mathieu. Agassi rallied for a 4-6, 3-6, 6-3, 6-3, 6-3 victory Monday in the French Open in Paris.

Then Agassi stopped rushing, became more creative and won 11 of 12 games, then after a lapse the last five games of the match. Mathieu suddenly looked like a rookie pitcher who breezes early in a game but gets roughed up on his third time through the lineup.

As Mathieu put it, reverentially and simply: “Hey, I had Agassi across the net.”

Next for Agassi in his quest for an eighth Grand Slam title will be 11th-seeded Juan Carlos Ferrero, who rallied to beat Gaston Gaudio 6-7 (3), 6-1, 6-7 (5), 6-2, 6-4. Ferrero lost to Kuerten in the semifinals the past two years.

Marat Safin topped Arnaud Di Pasquale 3-6, 6-4, 6-3, 6-2 to reach the final eight, where he’ll face Sebastien Grosjean, a 6-2, 7-5, 6-3 winner over Xavier Malisse.

For Agassi, it was the fourth time (all since 1996) that he won after losing the first two sets, and the prior occasion was in the same setting. In the 1999 French Open final against Andrei Medvedev, Agassi’s 1-6, 2-6, 6-4, 6-3, 6-4 triumph made him the fifth man to complete a career Grand Slam.

Both then and Monday, he was filled with the sort of grit that previous versions the “Image is Everything” Agassi or the married-to-Brooke-Shields-and-ranked-141st Agassi didn’t always demonstrate.

“Every time I think about things I could have done differently,” Agassi said, “I take a lot of pleasure in the fact that I’m still here doing things the way I want.”