In 2008, the fourteen-year-old Santos ran the 400 m in 53 seconds and he decided to take the sport seriously after running at the national schools championships. His performances attracted the attention of José Ludwig Rubio, a Dominican coach and former president of the national association. The following year he ran a personal best of 47.58 seconds and made his international debut at the 2009 Pan American Junior Athletics Championships. He was eliminated in the first round of the 400 m and was impressed at the speed of fellow Caribbean athlete Rondell Bartholomew. He broke his first national junior record at the competition as part of the Dominican 4×400 metres relay team, running a time of 3:13.18 minutes. A visa problem caused him to miss out on the 2009 World Youth Championships in Athletics.