JOHANNESBURG—As the second-lowest ranked team in the World Cup competition, South Africa is expected to lose its opening match Friday against Mexico. But to ensure victory, Michael Mvakali recommends a simple fix: a concoction of plants and animal limbs.

"You use the horse's foot and the ostrich leg, you mix it with some herbs and you put it on the players, on their knees and their legs, and when they kick, even the goalkeeper can't get hold of that ball," said Mr. Mvakali, a practitioner of traditional magic. While he hasn't...