Soccer on a Sunday (Magic Treehouse #52: A Merlin Mission) by Mary Pope Osborne - Hardcover

Goal! 

Jack and Annie have tickets to one of the most exciting soccer games ever—the 1970 World Cup! They are sure the famous soccer player Pelé will tell them a “secret of greatness.” The game is nonstop action and the stands are packed. But how will they find Pelé in a crowd of 100,000 soccer fans? Have they failed their mission? Or will the answer come when they least expect it?