In a scintillating match that set the center court at State Roland Garros ablaze in the gathering dusk, Paul McNamee, a fascinating 25-year-old Australian previously noted primarily for his doubles play, hustled and muscled John McEnroe out of the French Open tennis championships tonight in four tie breaker sets, 7-6, 6-7, 7-6, 7-6.

This 4-hour 18-minute epic was a grand triumph for McNamee, a superbly fit and uncommonly exuberant player who last year took the unusual step of dropping off the pro tour for four months and working eight hours a day to completely remodel his backhand.

Twelve months ago, McNamee was ranked 90th in the world. After scrapping his weak and defensive one-handed backhand for a two-fisted stroke that is neither a great weapon nor an insurmountable liability, he went through some rough days in singles after rejoining the tour.

But he persevered, ignoring colleagues who said he was a fool for sticking with the new stroke, and now says gleefully that "the benefits are starting to accrue." He currently is ranked No. 49, and will climb as a result of his gutsy, determined and ultimately glorious victory over McEnroe, who was seeded No. 2 here in the world's foremost clay court championship.

As the match went into its fifth hour, McNamee was still full of bounce and energy, bustling around the court and challenging the weary but equally determined McEnroe in scrambling, uncompromising, full-court points that thrilled and delighted the crowd of 15,000.

Running around his bankhand to hit his formidable topspin forehand at every opportunity, McNamee called on a seemingly inexhaustible source of vitality and the inspiration of the moment to outplay the more gifted McEnroe, who looked terribly weary in the fourth set but gave nothing away.

The match appeared headed for a fifth set as the left-handed McEnroe took a 4-1 lead in the fourth, then broke for a 6-5 lead and served for the set after McNamee had battled back to 5-5.

The 12th game was a classic, a kind of microcosm of the shifting fortunes of the match. It lasted nearly 20 minutes, and went to deuce 10 times. McNamee fought off seven set points -- some of them excruciating -- and finally broke through after McEnroe double-faulted to give him his fourth break point.

The Australian ran around a second serve to his backhand and nailed a forehand winner -- reverse cross-court, a foot beyond McEnroe's desperate forhand lunge -- as the upset-minded crowd broke into a spontaneous, deafening chant of "Mac-na-mee, Mac-na-mee."

Into the best-of-12-point tie breaker they went for the fourth time, and McNamee held firm. He was pumped up, physically and mentally, and ran the last five points from 22, breaking into a jubilant grin as McEnroe hit a tired forehand wide on the first match point.

The long day of struggles and drama on the red clay of Roland Garros -- perfectly typical of the physical and psychological endurance test that is the French Open -- had begun nearly 10 hours earlier, with last year's runner-up, Victor Pecci losing to Chilean Belus Prajoux in a match that had been suspended overnight.

Pecci, the handsome, 6-foot-4-inch Paraguayan who wears a diamond in his right ear, has been struggling this year. He had won only six matches in six tournaments, spending most of his time playing exhibitions as he tried futilely to adjust to a wood racket he had adopted for commercial reasons.

Two weeks ago, he went back to his old metal frame, but he has not yet found his form. His footwork remains sluggish, and he seems hesitant about when to stay back and when to attack.

Prajoux, who was sidelined most of last year with knee and wrist injuries, played more patiently. After failing to convert a match point and losing the third set tie breaker, 8-6.

He kept digging, playing smartly and well, and took another tie breaker, 7-5, to seal the match he had led overnight by two sets to love, 7-5, 6-4, 6-7, 7-6.

Other men who completed rain-delayed second-round victories included Guillermo Vilas, who routed Tomaz Koch, 6-2, 6-2, 6-3 and Harold Solomon, who methodically beat New Zealander Chris Lewis, 6-3, 6-3, 6-3.

Moving into the fourth round, along with McNamee, were Raul Ramirez, Hans Gildemeister, Yannick Noah, Jimmy Connors, Vitas Gerulaitis, Ferdi Taygan and Wojtek Fibak. Fibak dispatched Paolo Bertolucci, 6-1, 7-5, 7-5, then hurried off to see his fellow Pole, Pope John Paul II celebrate a historic mass outside Notre Dame Cathedral.

Connors again looked uncertain and vulnerable on the red clay, but he beat Antonio Zugarelli, 7-5, 6-4, 7-5. Zugarelli had a set point at 5-3 in the first set, and chances in the next two but played foolishly -- trying vainly to out-hit Connors in the crunch after getting there by soft-balling him and waiting patiently to reap the errors.

Ramirez, who is pulling out of a long slump, upset Eddie Dibbs, 6-3, 7-5, 6-5. Noah, runner-up to Vilas in last week's Italian Open and the Great French Hope as well as the Great Black Hope, aggressively and impressively cut down Californian Eliot Teltscher, 6-3, 6-0, 7-6, to advance to a meeting with Connors on Sunday.

Defending women's champion Chris Evert Lloyd cut down fellow American Pam Teeguarden, 6-1, 6-1, then confirmed that she has requested "wild card" entry to Wimbledon, which is three weeks away.

Interesting matches simmered and occasionally boiled all around the picturesque Roland Garros grounds. Two young Americans -- Van Winitsky (second round) and Ferdi Taysan (third) -- won matches from two sets down. Taygan going to 11-9 in the fifth to oust Frenchman Dennis Naegelen.

But all else paled in comparison to the titanic war waged by McEnroe, the knight of the woeful countenance, and the smiling, refreshing McNamee.

In its closing stages, this turned into a quintessential Roland Garros scene. The sun, which had popped in and out of threatening clouds all day, was dipping behind the steeply banked walls of the great stadium, which was colorfully packed to near capacity even though thousands of suppers undoubtedly were waiting.

The net cord judge had lone since put on an overcoat to ward off the chill evening breeze. The match was a gripping, thoroughly entertaining spectacle -- an exhausted, struggling champion against an inspired underdog, the two of them weaving the sort of great tactical tapestry possible only on slow clay. The points were long, varied, often enthralling, etched briefly on the salmon-colored court in skid marks left by hours of lunges and dashes and sliding "gets."

The crowd was solidly behind McNamee, an engaging fellow with a head full of dark, Harpo Marx curls. A former Australian junior champion, he didn't join the pro tour until he had earned a degree in statistics from Monash University in his native Melbourne, then completed half a course in law school.

He has studied Zen Buddhism, and obvioiusly enjoys the fast combat of the court. Pleasure was frequentlly evident on his face. Meanwhile, the dour McEnroe -- who, though only 21, has played a grueling schedule the last two years, and clearly is hampered by fatigue as well as a sore back, tender ankle and blistered racket hand -- revealed only pain.

Although McNamee did beat Stan Smith to win a small Gran Prix tournament in his adopted hometown of Tampa, Fla., this spring, most of his success has come in doubles with countryman Peter McNamara.

When it came down to the nitty-gritty, McEnroe raised the level of his game several times, and McNamee trumped him. He plays with an over-sized graphite racket, and used it like a big stick. Eventually, under the pressure, it was the more talented player who wilted and crumbled.

McNamee used to have a reputation of getting tight in tense situations, and beating himself. Last year at the U.S. Open, he nervously fritted away a match to Englishman John Lloyd in a fifth-set tie breaker. "I didn't want to come to the same fate today," said the 5-foot-10, 160-pound embodiment of the adage than an Australian might lose, but he never quits.

McNamee had definite strategic plans, formulated after losing a close match to McEnroe in Las Vegas last month. He kept the pressue on with his returns of serves, hitting intimidating forehands whenever possible. He kept pounding topspin at McEnroe's backhand, getting to the net behind it whenever possible, and ran like a deer, never showing any sign of weariness or lack of resolve.

Harry Hopman, who was the Australian Davis Cup captain in the glory days of Aussie tennis supremacy, was in the gallery, and wished McNamee well before the match. It was at Hopman's camp in Florida, and with his encouragement, that McNamee learned the two-fisted backhand with which he won a few critical points.

"Seeing Hoppy really gave me a lift," said the ebullient, instantly likeable McNamee, who also has taken to heart Hopman's old credo that fitness is a most valuable weapon.

The crowd was taken with McNamee, who says if he had not mastered the new backhand he would have quit tennis and gone back to law school. ("if you've got a weakness, and you want to get to the top, you've got to eliminate it . . Even if it means going through some heartbreak on the way."

At the end -- when he expanded as McEnroe drooped in the final tie breaker -- the impassioned French audience again broke into rhythmic clapping and chants of "Mac-na-mee, Mac-na-mee-," sweeping a joyous victor out of a magnificent arena on a heartfelt wall of noise.