Contreras reached the round of 16 at both the 1956 US National Championships and the 1957 French Championships. At the 1958 Wimbledon Championships he partnered with Rosie Reyes to make the semi-finals of the mixed doubles. He won a men's doubles gold medal at the 1959 Central American and Caribbean Games and was a mixed doubles gold medalist at 1963 Pan American Games, partnering Yola Ramírez.