 Only three teams competed and Cuba easily won, with Marrero contributing a victory in the only game he pitched.In the third Amateur World Series in 1940, Marrero led the Cuban team to victory, going 3–2 with a 1.15 earned run average (ERA), and was named the most valuable player of the series.In the fourth Amateur World Series in 1941, Marrero won three games, but the series ended in a tie between Cuba and the Venezuela team.