Dix turned professional in mid-2008, signing a multimillion-dollar contract with Nike. He reached the Olympic finals in the 100 and 200 m, and won two bronze medals; the only American track athlete to win two individual medals at the 2008 Summer Olympics. He suffered an injury at the 2009 US Championships, thus missing out on the World Championships, and a contract dispute with his agent resulted in only a handful of appearances that season. In 2011 he was both the 100 and 200 m American champion and won silver medals in the events at the 2011 World Championships. An injury at the 2012 Olympic trials meant he missed a second Olympic appearance.