In January 2011 it was reported that he would be joining Querétaro F.C. of Mexico's Primera División. However, he was not signed by the Mexican club. In late February 2011 he went on trial with Seattle Sounders FC of Major League Soccer in the United States. On 18 March 2011, following a successful trial, the club officially signed Rosales. During Rosales' first season with Seattle, he scored 5 goals in 26 appearances. Additionally, he assisted on 13 goals which was third overall in the league. His 13 assists also set a club record for number of assists by a single player in a single season. Rosales won the MLS Newcomer of the Year Award for the 2011 Major League Soccer season and was subsequently signed to a new, multi-year deal on 13 December 2011. In his three years with the club Rosales tallied 12 goals and 34 assists in league play. He also helped the club in capturing the 2011 Lamar Hunt U.S. Open Cup.