Castillo was a member of the National League All-Star team in 2003, his second career All-Star selection. He also led the Marlins in hitting and won his first career Gold Glove Award. Castillo was a central figure in the NLCS Game 6 comeback by the Marlins against the Chicago Cubs at Wrigley Field after a foul ball that he hit was knocked away from the Cubs' Moisés Alou by fan Steve Bartman. The Marlins went on to win that game, as well as Game 7, to get to the 2003 World Series, in which the Marlins defeated the heavily favored New York Yankees. This was the second World Series of Castillo's career, but the first in which he actually played.