On April 2, 2007, in his first official at bat, Dukes got his first major league hit with a solo home run to center field in the fifth inning against the New York Yankees. In his second game, he hit his second home run en route to a victory versus the Yankees. On December 3, 2007, Dukes was acquired by the Washington Nationals for left-hander Glenn Gibson, a fourth-round draft pick in 2006 who was ranked among the Nationals' Top 10 prospects according to various baseball sources, including prospect authority "Baseball America".