John McEnroe tennis' knight of the woeful countenance, lanced his Long Island neighbor, Vitas Gerulaitis, today 7-5, 6-3, 6-3, to win the U.S. Open -- the first Grand Slam singles title of his ascending career.

McEnroe, who pouts and grimaces and snarls while hitting shots that should make his opponent cry instead, is five months short of his 21st birthday, the youngest man to win America's premier tennis title since Pancho Gonzales in 1948.

The gifted but tempermantal left-hander from Douglaston, N.Y., less than 10 minutes from the National Tennis Center and five minutes from Gerulaitis' house in King's Point, made the final rather anticlimactic with his searing serves and volleys, and returns of serve that cut like a razor.

McEnroe lost his serve only once -- serving for the first set at 5-4 after having game points in seven of the first eight games -- and then lost only 12 points in 10 service games the rest of the match.

His only other moment of hesitation came when he served for the match, after the pro-Gerulaitis crowd of nearly 20,000 spectators screamed loudly for the sagging underdog in the yellow shirt and shorts that matched his shaggy, blond mane to make a comeback.

When McEnroe missed a first serve and steered a backhand first volley wide to fall behind 30-40 in the final game -- the only break point he faced in the last two sets -- his thoughts rewound to Saturday's semifinal when he was broken while serving for the match against injured defending champ Jimmy Connors.

"Certainly I got a little nervous at the end. That break point, I mean, if I'd lost that game Vitas would have been more in the match than Connors was," the champion said later.

"Connors never seemed to get any rhythm going, but Vitas, I mean a little thing like that could give him a lot more confidence, and he could start playing better. I'm just glad I was able to get out of that. He would have been a lot tougher if I lost that game."

But if there was a flicker of hope left in the flamboyant Gerulaitis, who came from two sets and a service break down to beat Roscoe Tanner on Saturday, McEnroe snuffed it out quickly.

A firm, assured forehand cross-court volley off a running forehand down-the-line by Gerulaitis got McEnroe back to deuce, and a netted back-hand return put him at match point for the first time.

He raised his arms and clenched his lips, as if to say "Now, God, please . . . don't prolong this." Then he followed a second serve to the net and made the sort of stretching, wonderfully athletic low volley that is his forte. Gerulaitis got to it, but his passing shot sailed wide.

As it did, McEnroe screamed and leaped three feet off the asphalt-based hard court, tossing his racket 20 feet into the early evening air. He turned and raised his arms trimuphantly to his family, seated beaming in a court-side box.

Gerulaitis -- who had won only nine games in two previous matches against McEnroe this year, but still thought this was his golden chance to win the Open after Tanner upset his nemesis, top-seeded Bjorn Borg, in the quarterfinals -- was obviously disappointed. He received the $19,800 runner-up's prize, turned quickly, and uncharacteristically said nothing.

McEnroe, after receiving the $39,000 winner's check and gleaming silver cup, spoke rather self-consciously, trying to force humor that didn't come off.

"This is by far my biggest win," he said at one point. "I'm sorry it had to be Vitas, because he's a good friend of mine."

If McEnroe was jubilant about adding the Open title to the Grand Prix Masters and World Championship Tennis titles he won earlier this year, he didn't show it. He was rather ill at ease and snippy in a postmatch interview. "I can't even speak right now," he began. When asked how he would celebrate, he said, "None of your business."

Although he played superbly in the final, wielding his racket as cuttingly as a street fighter with a switch-blade, McEnroe acknowledged that he had some luck earlier in the tournament. Two of his opponents -- John Lloyd and Eddie Dibbs -- defaulted with injuries, and Connors was inhibited by back spasms in the semifinals.

"Everybody was saying in the dressing room that I was going to win by default. I mean, two guys defaulted, Connors had a bad back or something. That's pretty incredible for a major tournament," said McEnroe. "So I'm just glad Vitas went out there and played lousy."

McEnroe had stayed sharp by playing doubles -- he and Peter Fleming added their first U.S. Open doubles title Friday to the Wimbledon title they won in July -- and he was in devastating form for the final.

He put savage pressure on Gerulaitis right from the start. He had three break points in the first game, broke in the third with a lovely backhand lob winner and running forehand down-the-line pass, had one break point in the fifth game and two in the seventh.

But McEnroe almost let the set he had so thoroughly dominated get away when he lost his serve for the only time at 5-4. At 30-15, Gerulaitis faked going down the line and made a great cross-court passing shot from deep in his backhand corner. Then he jumped on a second serve, got to the net, and put away a forehand volley. On the break point, McEnroe drilled a forehand volley five feet over the baseline.

The crowd was yelling for "Broadway Vitas" now, but he played a terrible game to lose his serve again, double-faulting twice in a row to 15-30 and mis-hitting a smash off a very short lob for the break.

Gerulaitis looked forlorn as he butchered that shot, and he had good reason to. McEnroe served out the set at love, including an ace for 30-0 and a service winner to the forehand on the first set point, and was never in any trouble again.

McEnroe had predicted beforehand that one decisive factor would be his ability to do more with Gerulaitis's second serve than Gerulaitis could do with his. He was right. Gerulaitis got only 51 percent of his first serves in the court, compared to McEnroe's 60 percent, but McEnroe hit the more punishing returns, either winning points outright or forcing weak volleys and half-volleys that had "pass me" written on them.

"My strongest attribute, when I'm playing well, is my serve and volley. If I can win that pretty easily, then I get confident on my returns and I start hitting those hard and then I just get into a groove where I start attacking a lot. And then all of a sudden, if I get up a break, if I'm playing well, it's tough to break me back," said McEnroe, generalizing about his game.

The assessment was right on the mark today. The better he got, the more he attacked. He hit some astounding half-volleys and lunging low volleys to stay in points, camped practically on top of the net, and then volleyed with such control of pace and spin that even the swift Gerulaitis always seemed a couple of desperate inches away from getting to the ball.