For an hour and 45 minutes last night, one of the best tennis players in the world was at the mercy of a little-known Frenchman named Gilles Moretton.

Moretton kept Ivan Lendl, the top seed in this week's D.C. National Bank Classic at Rock Creek Tennis Stadium, on a string until he missed a forehand in a second-set tie breaker of the second-round match. That point enabled Lendl to steal away with a surprisingly hard-fought 6-3, 7-6 (7-3) victory over the 109th-best player in the world.

In an earlier match, second-seeded Jose-Luis Clerc defeated 31-year-old Dick Stockton, 7-6, 6-1, to advance to the second round.

"Gilles is the kind of player who can miss the easiest shots and then come back and make the greatest shots," Lendl said. "Playing him is like being on a roller coaster.

"If he can come up with four great shots there's no way you can beat him."

That's exactly what Moretton, who wasn't even able to make his country's Davis Cup team, did with a fair degree of regularity through the first two sets. Offering more resistance than the fourth-ranked Lendl could have expected, Moretton used a strong serve and net game to come from behind in both sets, but really caused problems for Lendl in the second set.

In the process, he nearly continued the French hex over Lendl, who lost to France's Yannick Noah in both Davis Cup singles and doubles.

Lendl, who now has won 97 of his last 102 matches, survived a game penalty in the last set. With the score tied at five games apiece, Lendl hit a forehand into the net that gave Moretton the advantage. Upset at himself for having missed the shot, Lendl slammed his racquet against the court. He then was warned by the umpire, and moments later assessed a game penalty for delay. That gave Moretton the lead, 6-5.

Lendl never trailed in the second-set tie breaker, though Moretton was able to tie it three times. Lendl scored four straight points to turn a 3-3 tie into a 7-3 victory.

After falling behind, 2-0, in the first set, Moretton started serving with more verve and won the next three games. Over one stretch, he scored nine straight points. But Lendl retaliated by revving up his serve in the next game, and scored four straight points, the last on an ace, to tie. He then took the next three games to win the set.

Moretton continued to perform respectably in the second set, scoring on a couple of passing shots to break Lendl's serve and go ahead, 3-2, then holding serve to take a 4-2 lead. But after Lendl held serve to make it 4-3, Moretton lost his momentum in the next game, letting several shots that just failed to clear the tape on the net frustrate him.

Considering that this tournament has been billed as a showcase for young stars, its oldsters didn't do badly yesterday.

Jaime Fillol, 36, won two tie breakers to upset 12th-seeded Paul McNamee, 7-6, 6-7, 7-6. Three times he came from three or more games down, and received a standing ovation at the end of the three-hour match.

Bernard Fritz, who by tennis standards is almost ancient at 29, got the only other upset in singles with a 6-3, 6-2 victory over seventh-seeded Eddie Dibbs, no youngster himself.

Dibbs, who, like Lendl, was given to an occasional temper tantrum, was fined $500 for smashing his raquet and received a penalty point in his match.

In first-round matches yesterday, No. 8 Mel Purcell survived an early challenge from Pender Murphy to win, 7-6, 6-2. And Bernard Pils of Austria advanced to meet Clerc with a 7-5, 7-6 defeat of Skalke Van Der Merwe of South Africa.

And in a major upset, the world's top-ranked doubles team, Sherwood Stewart and Ferdi Taygan, lost to two Junior Davis Cup players, Mike DePalmer and Mike Leach, 2-6, 7-5, 7-5.

Clerc, who is on a binge similar to his mid-summer streak of four tournament championships last summer, now would seem to have an easy path to the final, until he possibly runs up against 10th-seeded Pablo Arraya in a quarterfinal match.

And though he concedes he is a little tired from his recent excursions in Europe, including a victory in the Mercedes Benz Cup last week, conditions seem favorable for him to make the final.

The Argentine advanced to the final of the Washington Star International in the similarly unkind July heat the last two years. If form holds true, his likely opponent in Sunday night's final will be Lendl.

Clerc went on top, 4-2, in the first set, but Stockton held his serve twice and broke Clerc to pull ahead, 5-2. At that point, Clerc took over, winning the next three games to take the set, then winning the first four games of the second set.