 Hannahan was traded to the Seattle Mariners for pitcher Justin Souza on July 11, .With the Mariners holding an 11–5 lead over the Kansas City Royals on August 6, Seattle manager Don Wakamatsu substituted Hannahan for shortstop Jack Wilson, who was experiencing minor discomfort in his right triceps area.This marked the first time Hannahan played shortstop at the major league level.