Moreno began his career at Club Blooming and then played for Colombia's Independiente Santa Fe before spending two seasons at the English club Middlesbrough. The rest of his career was spent at D.C. United apart from one season at the New York MetroStars in 2003, and he was the all-time leading scorer in Major League Soccer at the time of his retirement in 2010. On 22 August 2007, in a match against the New York Red Bulls, he scored his 109th MLS goal, surpassing the previous league record set by former Dallas Burn and Real Salt Lake forward Jason Kreis. On 17 April 2009, Moreno became the first MLS player ever to reach the mark of 100 goals and 100 assists when he assisted on a Ben Olsen stoppage time goal.