One of the tactics proselytizers use to try to convert nonbelievers is the appeal to fear. What if you're wrong? What if it turns out there really is a god and you've lived your life on the assumption that there isn't?
Perhaps only the most fundamental of theists actually believe that it was Manny's prayers that got him to win fight after fight from one weight division to another. The moderate theists, on the other hand, probably believe that prayer has at least some bearing on his game, complimenting his hard work and preparation, so if he ever should come face to face with an equally skilled fighter, prayer would tip the balance to his favor.