India, July 19 -- The World Cup final appears, at first glance, to have been arranged by football's instinct for theatre. Lionel Messi, aged 39, stands one victory away from completing an unprecedentedly graceful farewell. Across from him is Lamine Yamal, 20 years his junior, carrying the promise of everything the game might become after Messi has gone.

Yet the more intriguing master-and-prodigy confrontation will unfold several metres beyond the touchline.

When Argentina meet Spain in New Jersey on Sunday, Lionel Scaloni will attempt to defend the World Cup against Luis de la Fuente, one of the instructors who helped educate him as a coach. Before Messi confronts his possible successor, therefore, the pupil must overcome the professor....