John McEnroe's convincing victory over Bjorn Borg in the final of the U.S. Open Sunday represented a changing of the guard in tennis both on and off the court.

By beating Borg in four sets, McEnroe firmly established himself as the No. 1 player in the world. That was not a major surprise.

The real surprise was that it was Borg, not McEnroe, who left the tournament amidst a swirl of controversy; Borg whose behavior was questioned by some and Borg who yesterday canceled two highly publicized public appearances in New York, claiming through his business manager that he was ill.

Notwithstanding the death threats against Borg Saturday and Sunday, his exit after the final was viewed by many as less than gracious at best, rude at worst.

"He hadn't even been told about the threat when he said he wanted to leave," said one USTA official. "He just said to the police (NYPD plainclothesmen) and security guards, 'Go to the locker room.' "

After the first threat Saturday, Borg came to the interview room, even lingered there, after a convincing victory over Jimmy Connors.

His departure from the National Tennis Center Sunday night was almost bizarre. After being escorted to the locker room -- which was barred to the press -- he was led down a back stairway, through a darkened kitchen, through a yard filled with garbage cans, to the parking lot. His wife Marianna and several other relatives were already en route to Borg's new house at Sands Point, Long Island. Borg and his coach, Lennart Bergelin, left in a Volvo station wagon.

While Borg fled, McEnroe was playing the role that used to be the Swede's: the gracious winner. He refused to say his dominating victory meant he had finally mastered Borg, pointing out that, "He would still beat me on clay. On other surfaces, I feel pretty comfortable against him. I think I can anticipate his shots pretty well here (on asphalt DecoTurf II) and on grass. But on clay, I can't beat him right now."

One writer suggested to McEnroe that he was being modest.

"I guess you haven't seen me play on clay lately," McEnroe cracked.

McEnroe is not a bad clay-court player but Borg, Ivan Lendl, Jose-Luis Clerc and even Guillermo Vilas, past his peak, would have to be rated better on the surface.

In the past, that has not really concerned McEnroe. But having conquered Wimbledon, having won three straight U.S. Opens, having beaten Borg in the finals of the last three major tournaments, it would seem his next logical step would be to try to improve his game on clay; at least to the point where he could challenge for the world's third major title, the French Open. This year, McEnroe lost to Lendl in the French quarterfinals in straight sets.

"It has never been important to me before," McEnroe said. "Maybe one of these years it will be. I've always just gone over to the French the week before it started and hoped for the best. Maybe next year, I'll do it differently."

McEnroe might play in the Italian Open, which is just below the majors in prestige, as a warmup for the French.

That is in the future, however. For now, at 22, McEnroe is the first player since Jimmy Connors in 1974 to hold the world's top two titles in the same year.

Borg, 25, has reached a crossroads in his career. He has tried 10 times to win the U.S. Open and failed each time, four times in the final. Some think he may never win the championship, a major flaw in an otherwise remarkable record.