 Horton made his debut as a senior (despite still competing as a junior) in 2002 competing at the U.S. National Championships in Cleveland, Ohio where he placed first on rings and vault, placed second in the all-around and the floor exercise, and tied for fifth on the high bar.In 2003, he competed in the Winter Cup challenge, where he qualified to the individual event finals.Later that year he was chosen to compete for US at the Pan American Games in Santo Domingo where the men's team won bronze and he placed fourth all-around.