In 2005, Cotts went 4–0 while appearing in 69 games, throwing 60.1 innings, compiling a 1.94 ERA, striking out 58, and yielding just 1 home run. MLB.com awarded him the "Setup Man of the Year Award", an award determined by fan voting. In the American League Championship Series, he was the only White Sox reliever to appear in Chicago's 4–1 series win, throwing 2/3 of an inning in Game 1. Cotts pitched in all four games of the World Series and was the winning pitcher in Game 2.