A sweaty, red-faced John McEnroe faced the hot television camera lights and a barrage of questions about why he almost lost the first round of the U.S. Open last week to unseeded Israeli player Shlomo Glickstein.

Was it your knee, John? There had been stories that his new love life was plaguing his play. Was he getting old or bored?

More than 2,000 miles away in the corporate offices of Nike Inc., some company officials probably were asking themselves the same questions. After McEnroe lost early at Wimbledon and barely squeaked by his first match at Flushing Meadow, his fans probably weren't the only ones sitting on the edge of their seats watching every double fault and deuce game.

How well McEnroe plays and what tournaments he wins are important to the earnings of companies such as Nike, whose products are endorsed by McEnroe, the tennis giant who since April has helped sell $9 million in tennis shorts and shirts wholesale for Nike Inc.

"The best players in the world do not play perfect tennis every day," said Nike spokesman Chris Van Dyke, after McEnroe's near defeat. "He hasn't lost his number-one ranking. At this point, we're not concerned."

Sports is entertainment, but sports is also business, to which the U.S. Open, which started last Tuesday, can attest. Not only are there walking billboards such as McEnroe -- who, because of his contract with Nike, must wear Nike shoes, socks, shorts and shirts every time he plays -- but the stadium where McEnroe played also is dotted with signs advertising Clairol, Kodak, Equitable Financial Services, Burroughs Corp., Avis, Nabisco and Virginia Slims and Marlboro cigarettes.

A long backhand shot bounced the ball off of the green-and-white official clock with Omega written on it. The ball boys and girls wore green, blue and white uniforms and socks with the logo Fila emblazoned across them. Even the statistics sheets passed out to reporters advertised that Burroughs Corp. had supplied them.

A spectator asked a bartender wearing a Banfi Fine Wines apron if she could have her white wine in a glass larger than the little plastic cup he offered. "Sorry lady," he quipped. "This is the official wine-drinking glass of the U.S. Open."

To have their names connected with the prestigious tournament, companies donated equipment and paid fees ranging from $50,000 to $300,000. The U.S. Open wanted televisions. It got as many as it needed from Sony, including a 20-set monument to technological tennis in the center of the National Tennis Center that gives match results and locations and allows viewing of some of the games in progress.

The U.S. Open needed cars. Avis provided a fleet, plus wholesome-looking drivers in red-and-white Avis tennis shorts and shirts.

Not only is business overt, but a lot of financial deals also are sewed up in the boxes bought by companies and at the parties hosted by sponsors.

"It's a business event," tournament spokesman Ed Fabricius said of the games. "I've had people tell me they've sold more here in two weeks at the Open than they do all year" by wining and dining clients.

And there are stalls selling everything from strawberry shortcake to shirts. These stalls, most under yellow-and-white striped canopies, are "tremendously" important to the tournament, Fabricius said. "All you have to do is stand around and buy things. I'd like to have just the Italian ice concern. Those kids make $100 a day."

Bidding to become a sponsor of the U.S. Open starts years in advance. Many of the companies have long-range contracts and have been affiliated with the tournament for years, Fabricius said, adding, "Most of the time, they come to us." Cash donations from the companies cover prize money for the matches, he said. For example, Avis sponsors prizes for the men's singles championship, Fabricius said.

"It depends on what we need," he said. "In some cases, it's cold cash, and they get certain privileges" for their donations, such as boxes at matches and the opportunity to throw parties for clients.

"We may want services," Fabricius said. Avis has donated about 30 cars and drivers for players and VIPs. Fila Sports donated cash and uniforms for the ball boys and girls.

"These companies, they can buy boxes and things. It's a great way to entertain customers," Fabricius said. Without businesses, "We're in trouble."

For example, where would the tournament be without Sony Corp. of America and the 105 television sets it donated? Twenty new 25-inch Sony Trinitron televisions, which would retail at $1,999.95 each, are used in the match-in-progress electronic center outside of the stadium, and other televisions that would sell for as low as $599.95 are scattered around restaurants, the players' lounges, the press box and the referees' room as well as in the multitude of hospitality suites.

Speaking of hospitality suites, Sony has one of those, too. "It gives us a very good opportunity to entertain dealers and suppliers and people we work with on a regular basis and provide them with an evening of tennis," Sony spokesman Fred Wahlstrom said.

Having Sony televisions around the National Tennis Center "gives us very high visibility, and we think people who come to the tournament are people who would buy Sony equipment," Wahlstrom said. "In terms of numbers, they have over 100,000 people who go through there." Then there's the prestige of being associated with the sporting event.

As a grand finale, Sony is sponsoring a celebrity press tournament pitting sports reporters against celebrities such as comedian Alan King on one of the U.S. Open's last days, Wahlstrom said. Players Vitas Gerulaitis, Virginia Wade and Peter Fleming will act as reporters, using Sony's new video cameras and other equipment.

Restaurant bookings are handled by a New York catering concern. Most of the nonfood stall business is handled by Feron's, an East Coast sporting goods store. It leases booths for different tennis-wear companies as well as for CBS Sports, which was hawking shirts and hats imprinted with its logo.

Feron's employs about 95 salespeople and 15 managers for the tournament, and sales during the event's two weeks constitute a substantial part of the company's business. T-shirts imprinted with "U.S. Open" are the most popular item. They start at $11.99.

Feron's recently added Adidas and Izod La Coste to its list of vendors, which already includes Wilson, Bard, Stolle Emerson Tennis, Yonex and Ellesse, said Richard Tilker, Feron's vice president.

"We're very selective about who we let in" as vendors, Tilker said as he rushed around the company's U.S. Open headquarters under the stadium and past another Sony television showing the McEnroe-Glickstein match. "We're looking for people who are in the tops of their field."

When Nike found McEnroe to endorse its products seven years ago, he was not quite at the top of the tennis field, Van Dyke said. However, people in the early 1970s "saw him as an up and coming star. They saw raw talent, he would eventually be the number one seeded player in the world."

If McEnroe fell to number two, Nike would not drop his testimonials, Van Dyke said. "John is popular and well-known, not simply because he is number one. He goes after the game with enthusiasm."

McEnroe is independent, flamboyant and strongly athletic, all criteria the Nike people like. Van Dyke said that it was difficult to quantify how much money McEnroe has made for Nike, and he would not disclose the value of his contract.