From his second season onward, Curtin would anchor a starting spot in the Fire's centerback tandem, started 22 games and played 2,121 minutes. Curtin started every game for the Fire in 2003, playing alongside Carlos Bocanegra and helped the team's defense compensate for Bocanegra's loss in 2004. He would go on to play in more than 200 games for the Fire, which included U.S. Open Cup championships in 2003 and 2006. He was also named 2004 MLS All-Star and the March of Dimes/Comcast Athlete of the Year in 2005.