Hyped as a rematch of David vs. Goliath, Robert “The Ghost” Guerrero plays the role of an unassuming, God-fearing underdog when he takes on the motor-mouth king of boxing, Floyd “Money” Mayweather. Their Las Vegas superfight, this Saturday at 6pm on Showtime (pay-per-view), has been in the making ever since Mayweather signed a new contract in February with the cable network. But for Guerrero, a South County native of Gilroy, landing a bout of this magnitude has been an elusive quest.

Now 30, Guerrero was supposed to arrive at this point in his career years ago. When I first met him in 2007, he was still a kid. He hadn’t yet dealt with his wife, Casey, nearly losing her life to leukemia; or sitting out a year in a contract dispute with a former promoter; or having talking heads question his toughness after a cut prematurely ended a title fight at HP Pavilion; or relinquishing his title belt to take care of Casey and their two children; or suffering a torn labrum in his southpaw shoulder just weeks before the biggest fight of his career.

Over the course of several years, he went from a lightweight to man carrying the weight of the world on his shoulders. And he never stopped. Instead, Guerrero and his support system, which includes his father, Ruben, as his trainer, devised plans to claim titles—in four different weight classes, so far—and steadily move up divisions. When Casey’s cancer went into remission, Guerrero recommitted himself to the sport. When it became clear that premier fighters wouldn’t come to him, Guerrero bulked up to welterweight (140-147 pounds) and approached them.

So, now, when the Showtime cameras flick on and Mayweather confronts Guerrero like fresh meat in the prison yard (and Mayweather knows how this plays out, having spent last summer behind bars for beating his ex-girlfriend in front of his children), the confidence and patience of the latter is as laid-back as a sling. “Act all crazy, say what you want. You’re not intimidating me,” Guerrero says. “And that’s what he’s all about. In this game, psychological warfare is big. You can break a fighter in press conference, and you’ve already won.”

Guerrero’s record is almost as good as it gets—31-1-1, with 18 knockouts—while Mayweather’s record IS as good as it gets: 43 wins, 0 losses and 26 KOs. Even at 36, Mayweather is considered a sure thing, and he makes sure to let everyone know it. A Guerrero victory would be an upset of Davidian proportions, only David was wise enough to stay the hell out of arms’ reach. The Ghost, by contrast, will only win this battle by fighting inside-out.

And yet, while admitting that Mayweather is “one of the best pound-for-pound fighters ever,” Guerrero is confident his past has prepared him for the present. “It prepares you for life, it prepares you for everything,” he says. “When you’re ready mentally, nothing can stop you.”