For John McEnroe, this was the ultimate.

Treated like a hero for one of the few times in his life, he played his best tennis in the clinches today and finished an extraordinary year by winning the Davis Cup for the United States.

What made this final victory so sweet for McEnroe was the help he received from the Riverfront Coliseum crowd of 13,327 near the end of the match. Urged on by the cheering, stomping fans, McEnroe dominated the last set to beat Argentina's Jose-Luis Clerc, 7-5, 5-7, 6-3, 3-6, 6-3, in a 4-hour 8-minute test of grit, stamina and skill.

His victory gave the U.S. an insurmountable 3-1 lead in the final round. The final margin was 3-1 as a now meaningless fifth match between Roscoe Tanner and Guillermo Vilas was called by mutual agreement with Tanner leading, 11-10, on service in the first set. The Americans will split $200,000 in prize money posted by a Japanese company; the losers split $100,000.

The victory, McEnroe's third in three days, also meant that in one year he won Wimbledon, the U.S. Open and three points in the Davis Cup final. The last American to complete such a triple was Don Budge in 1937. The last foreigner to do it was Australia's Frank Sedgman in 1952.

"The last set, I was really pumped up," said McEnroe, sipping a beer in celebration. "It's easier to get emotional when you have the people behind you like that. It wasn't a personal thing for them; it was the United States versus Argentina. I thought it was great."

McEnroe's serve, always his most important weapon, carried him in the last set. In five games, McEnroe lost four points on serve. He put 17 of 23 serves into play and won 16 of those points.

"In the fifth set, he was serving really well," Clerc said. "Maybe I let him get his confidence when he broke my serve."

That crucial final break came in the fourth game, at love. McEnroe began by hitting a deep backhand return that Clerc reached but could not get back. Sensing a slight dip in Clerc's resolve, McEnroe followed his opponent's weakening second serve to the net and punched a forehand volley into the corner for 0-30. For emphasis, he punched his fist through the air.

Unnerved, Clerc double faulted for 0-40. He came back with a hard first serve, but McEnroe scrambled. Surprised to see the ball come back, Clerc volleyed long. McEnroe jumped a foot into the air and screamed, "Yeah!" as the crowd leaped to its feet, crying "U-S-A!, U-S-A!"

McEnroe was playing with a passion now. He was never in trouble the rest of the match, the last game being his exclamation point. He served five rockets. On the first, he butchered an easy volley, but the last four were all his, Clerc barely touching the final serve.

As the last serve slithered off the wood of Clerc's racket, McEnroe leaped into the air, let out a whoop, and jumped the net to shake hands. He threw himself into the arms of U.S. Captain Arthur Ashe and trainer Bill Norris, then turned to the crowd with both arms and index fingers upraised. Finally he hugged every one of his teammates.

"It was a great feeling for me," McEnroe said. "I've had a long year and the last set I really felt tired. But the adrenaline kept me going.

"I thought he played very well. He surprised me the way he played on this (Supreme Court) surface. He really hung in there. The fifth set I had to play my best tennis and serve really well to beat him. I thought he played a helluva match."

From the start this was a superb match. If there were bad feelings from Saturday's volatile doubles match, they never showed.

McEnroe, who at age 22 is the dominant player in the game, had minimal problems today with the officials and with Clerc.

Once, chair umpire Robert Jenkins admonished him for slamming a ball high into the stands in frustration. Once, referee Kurt Nielsen gave Ashe a "friendly warning" after McEnroe yelled at one of the service judges.

"But, really, he didn't give you all much to write about his behavior today," said Ashe, who led the U.S. to its 27th Davis Cup in his first year as captain. "I really thought he was pretty good."

McEnroe was very good at his game. At 23, Clerc has become one of the world's top players (ranked No. 5) on any surface. His serving and volleying have improved greatly and, like McEnroe, he is an outstanding competitor, capable of coming up with big shots on big points.

Today, he had McEnroe down a break in the opening set. But, with Clerc serving at 5-4, McEnroe played one of those virtuoso games he seems to produce at crucial moments to even the set at 5-5.

He held to lead, 6-5, and broke Clerc in the following game when Clerc made two unforced errors to give McEnroe the set.

McEnroe had a chance to take control of the match in the second set. They were on serve with Clerc serving at 4-5 when McEnroe had three set points. But on each one he made an unforced error, allowing Clerc to escape the game.

"What I did there is what you call a choke," McEnroe said. "It wasn't anything that he did, it was just me. I really let him get back in the match that way."

Buoyed by that game, Clerc broke McEnroe in the next game, finishing it with a brilliant cross-court backhand that left McEnroe holding his head. Clerc then served out the set.

"I was getting my confidence then," Clerc said. "I thought I played very well against him. I thought I could win."

When Clerc broke McEnroe in the third game of the third set, there were many here who thought his chances quite good. But from 1-3 down, McEnroe won five games in a row, breaking Clerc twice to win the set, 6-3. He finished it with an ace and went to the dressing room for the break seemingly in command.

"I wanted to come back and jump on him quickly, get in control right away," McEnroe said. "Instead, he did that to me. He really surprised me with his aggressiveness."

Clerc won the first three games, getting a 5-1 lead. So it came down to one final set. Ashe was confident. "John's a very good fifth set player, especially on a fast surface," he said. "I know he felt the pressure. It's very tense out there. Each time you change courts, the Davis Cup is staring you right in the face. We all knew what the stakes were."

McEnroe and Ashe did not want the decision to come down to a fifth match. And McEnroe wanted this one because the Davis Cup is very important to him.

In that final set he produced some of his most remarkable tennis in an already remarkable year.

"That's the first time I've ever had to play a fifth set on the final day," said McEnroe, who has been on three winning cup teams. "I guess I played my best when I needed to. I felt the pressure but I also felt the crowd behind me. That was a good feeling. I can't say enough about the people here this weekend."