It took Amelie Mauresmo 12 years to win her first Grand Slam title. She may need another dozen to figure out how to win in Paris.

Mauresmo, the no. 1 player in the world since winning the Australian Open earlier this year, bowed out of the French Open yesterday, losing her nerve and her form in a 6-7(5), 6-1, 6-2 defeat at the hands of talented Czech teenager Nicole Vaidisova. Vaidisova played well, but Mauresmo’s woeful performance determined the outcome. She seemed to be fighting back tears in the final set.

The victory put the 17-year-old Vaidisova in her first Grand Slam quarterfinal, though she was not the only woman to accomplish that feat yesterday. Dinara Safina, the 20-year-old sister of Marat Safin, and Anna-Lena Groenefeld, a 20-year-old German, both find themselves farther along in a major tournament than ever before.

Safina continued her excellent claycourt season with a spectacular victory over Maria Sharapova. After falling behind 5-1 in the third set, Safina won 24 of the next 30 points, dealing Sharapova perhaps the worst loss of her career, 7-5, 2-6, 7-5. Sharapova committed 63 unforced errors, including 33 in the first set and 17 after she led 4-0 in the third.

Also through to the quarterfinals were defending champion Justine Henin-Hardenne, Venus Williams, Kim Clijsters, and Svetlana Kuznetsova. One quarterfinalist will be decided today, as Martina Hingis resumes her delayed match against 19-year-old Shahar Peer, who is seeking to become the first Israeli woman to reach the quarters of a major.

For Mauresmo, all seemed well after she closed out the first set and skipped to the sideline, pumping her fist. She had blown a 5-2 lead and survived, something she might not have done before Australia.

The rest of the way, however, Mauresmo was abysmal.After hitting 14 winners and making 11 unforced errors in the first 13 games, the 26-year-old Frenchwoman hit only 11 winners and committed 20 errors in the remaining 15 games. Her backhand was particularly troublesome, floating long when she sliced and sometimes flying off the frame of her racket when she tried to dull Vaidisova’s power with looping topspin.

“It’s disappointing but I think I still have to improve on clay,” Mauresmo said afterward. “Maybe people shouldn’t expect much of me on clay.”

Fair enough, but defeating Vaidisova was not much to expect. The 6-foot teen has been a top prospect for more than two years now – she won her first singles title at age 15 – but her brand of slugger tennis, and her less-than-fleet feet, are more suited to hard courts. No matter how many 115 mph serves, flat forehand drives, and two-handed backhand bullets Vaidisova hit, the usually steady and more experienced Mauresmo should have succeeded in moving her around the court and knocking her off balance. Witness their last meeting, in the fourth round in Australia, where the hard courts also play slowly: a 6-1, 6-1 victory for Mauresmo.

Now that Mauresmo is out, one has to like Williams’s chances even better.The last American in Paris played a shaky first set against Patty Schnyder yesterday,committing 19 errors before finding her rhythm in a 4-6, 6-3, 6-2 victory. Williams played her best tennis of the tournament in the last two sets, making more than 70% of her first serves, winning 12 of 14 points at the net, and limiting her errors to 13.

Against Vaidisova, Williams’s athleticism and ability to apply pressure should prove the difference. Next in line would be Kuznetsova (who defeated Francesca Schiavone 1-6, 6-4, 6-4) or Safina. Though both Russians are more comfortable on clay than Williams is, they are erratic and less proficient in tactics. If Williams continues to cover the court as well as she has to this point, and move forward when opportunities arise, she should find herself in Saturday’s final.

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James Blake surprised us twice at the French Open this year. America’s best tennis player looked phenomenal in a second-round victory over Nicolas Almagro, the third-best player on clay this season. While Blake could hardly have been the favorite to win that one, he should have prevailed over Gael Monfils, the 19-year-old Frenchman whose 6-2, 6-7(2), 7-6(1), 5-7, 6-4 victory has his hometown fans hoping for a quarterfinal date with Rafael Nadal. Monfils has now won three straight five-set matches here; Blake fell to 0-8 in his career.

Blake, ever the sportsman, said Monfils was the best athlete he had ever played against – strong words from a man who covers the court as well as anyone.Yet Monfils is nowhere near the tennis player Blake is. The 6-foot-4 Frenchman nearly won all four major titles in a year as a junior, and one can imagine that he did not have to worry too much about strategy because he moves so effortlessly, both on hard courts and on clay. A few years from now, a mature Monfils might be something to behold. Yesterday, however, Blake should have carried the day.He missed the easiest of volleys on break point at 4-4 in the fifth set and seemed unduly distracted by the partisan Parisian crowd.

Monfils’s next opponent, Novak Djokovic, has the potential to one day be the no. 1 player in the world. The 19-year-old Serbian defeated Monfils at the U.S.Open last year,though he irked Monfils, and onlookers, by taking numerous injury timeouts in the fifth set. The Frenchman says all has been forgiven and the two are now friends.

It should be an excellent match. Djokovic has looked stronger so far, but playing at home ought to help the energetic and charismatic Monfils, especially since he is now farther along at this tournament than most had predicted.

tperrotta@nysun.com