See main article: 2004 Italian Open (tennis).
Carlos Moyá defeated David Nalbandian in the final, 6 - 3, 6 - 3, 6 - 1 to win the men's singles tennis title at the 2004 Italian Open.
Félix Mantilla was the defending champion, but lost in the second round to Mariano Zabaleta.
A champion seed is indicated in bold text while text in italics indicates the round in which that seed was eliminated.