Castillo played well in the post-season. He had two RBIs in the 1984 American League Championship Series, including the game-winning, pennant-clinching RBI in Game 3, knocking in Chet Lemon for a 1–0 victory, sending the Tigers to the World Series. Castillo also caught the ball at third base for the final out of the pennant-clinching game in 1984. An article in The Detroit News several years ago questioned whether Castillo still had the ball.