ANY NEWCOMER WHO CAN DEFEAT JIM COURIER AND Andre Agassi bears watching. But when Jan-Michael Gambill upset both superstars at a 19.8 tournament in California, modeling agents tossed their business cards onto the court. The 6'4" blond, blue-eyed Gambiil now has his own $35 calendar and has shot an Adidas commercial. He also has moved into the upper reaches of the Association of Tennis Professionals Tour rankings, last year hitting No. 31. For those who aren't wise to him yet, Gambill, 22, has a trick up his sleeve that pulls in new fans. "When it gets hot, I practice shirtless," he says. His friends don't buy that explanation. "The shirt is never on unless it has to be," says Courier, 29. "He's running around in his shorts and sweating. Women tend to like that." Gambiil keeps them happy by enduring a punishing daily regimen that includes 90 minutes of weight training and up to 1,000 stomach crunches. "My abs are one of the features I work hardest on," he says, although "a couple of ladies at one of the tournaments gave me the 'best butt' award, which was pretty funny." Gambill's mother, Diane, 47, who named him after 1970s heartthrob actor Jan-Michael Vincent, has seen her son's groupies in action. "He's very noticed—every, part of him," she says. Gambill, who started playing tennis at age 5, still lives on his family's 10-acre ranch outside Spokane, Wash., where his dad, Chuck, 53, serves as his coach. In his spare time he bottle-feeds wildcat cubs at a nearby zoological center. "I've always been fascinated by big tigers and lions," says Gambill. "Their beauty is just amazing." He's equally proud of his own. "I think it's healthy to look in the mirror," he says.