The whiz-bang theory here at Wimbledon is that Bjorn Borg simply grew weary of fame, grew weary of counting his money, grew weary of being stoic all the time, so he announced he wouldn't play again this year. Then, the whiz-bang theory goes, he shaved neatly, threw away his head band, put on a smile and introduced himself to the world, the way the king put on the beggar's clothes, as a poor young unknown named Mats Wilander, only freshly out of a village in the south of Sweden.

You got anything that makes more sense?

Here is Mats Wilander, who a month ago existed only in the minds of tennis zealots and suddenly he wins the French Open, after which he claims to be 17 years old and says he is fed up with questions such as, "Are you the next Borg?"

"I am not Borg No. 2," he said over and over. "I am Wilander No. 1, and that is enough for now."

One might sensibly expect a generation to pass before we would see the likes of Bjorn Borg again. It was Borg who, nine years ago, won the French Open at 17 to arrive on the international tennis stage a full-blown star. Later he would win Wimbledon five times in a row. People who know called him the best tennis player ever.

Now comes Wilander. Another Swede 17 years old. Another powerfully trim athlete with a two-handed backhand. Another computer on court, passionless in its destruction of an enemy's game.

Of four young Swedes here for Wimbledon, all too young to buy a beer, every one with blond hair curling to the shoulders, all cast in the image of Borg so precisely it is eerie, Mats Wilander today was set apart from these clones by one circumstance.

He set foot on Centre Court.

Wilander No. 1, indeed.

"I thought it was going to be very exciting," he said. "It is the most famous court in the whole world."

A little smile.

"But I was not nervous."

With royalty on hand among the 10,000 customers in the Wimbledon stadium, the kid from Sweden, making his first footprints on turf made holy by Tilden and Laver, was not nervous. He won in four sets from Heinz Gunthardt.

So although Wilander's reputation, such as it is, has been made on clay courts, he demonstrated today he is capable of winning on grass. His first serve is no cannon shot, yet it is serviceable. His second serve is noticeably weak and vulnerable to attack, a defect that once limited Borg, too.

Nothing else is weak. Wilander's two-handed backhand froze Gunthardt in his tracks. On the forehand side, which Gunthardt made the mistake of underestimating, Wilander once threw three straight winners down the line.

"Wilander could win here," said Dennis Ralston, the Wimbledon runner-up in 1966 and now Chris Evert Lloyd's coach. "He's not as good a server as Borg yet, but he's a better volleyer. In the French, he knocked volleys off very well."

In the French, he knocked everything so well that, unseeded, he beat the Nos. 2, 3, 4 and 5 seeds to win--names, Ivan Lendl, Guillermo Vilas, Jose-Luis Clerc and Vitas Gerulaitis.

Of the few hundred thousand people surprised by all this, we may include Wilander's coach, John Sjogren.

"I know he can beat one of those top players, but to beat four . . ."

Was the coach surprised?

"Sure," he said.

As sign of Wilander's precociousness, the young fellow seemed less amazed by his work than the coach was. Of today's match with Gunthardt, for instance, Wilander said, "I thought it would be more difficult." Someone then asked, "Have you looked ahead in the draw to see who you play next, and then who, and then who?"

This is a noble-savage question. The idea is that here's a farmer's son who found a tennis racket along the cow path and hit apples with it. But Wilander's answer was worldly wise. "Yeah, I've looked ahead. I know who I play."

He could not even act the noble savage.

"Everybody does."

Born in a village outside the southern Swedish industrial city of Vaxjo, Wilander is the son of a foreman at an air-conditioning factory. He first played tennis at age 10, according to Sjogren, but Wilander says, "I developed my two-handed backhand before Borg was becoming famous."

That makes him an 8-year-old with a bomber's backhand. Nine years later came the questions he has heard, in one form or another, 100 times in the last three weeks. Is he Bjorn Borg made young?

"Actually, I don't care about it," Wilander said of the comparisons he can avoid only by building his own record for a decade. "It doesn't matter to me. I believe it is very stupid to compare anyone with Borg, because he is one of the greatest players in the world."

Does it make him happy to be compared to such a player?

"No, it doesn't," Wilander said.

The kid has no grand goals this fortnight. "My ambition here is not that high," he said. "It takes a long time to get used to grass."

This is Wilander's second Wimbledon. He lost in the third round last summer.

Bjorn Borg? He won Wimbledon in his fifth try.