Born in Mexico City in 1934, Contreras completed his studies in California, attending Modesto Junior College.

[2] Along with his Modesto teammate Joaquín Reyes, he went on to play college tennis for the University of Southern California and the pair combined to win the 1955 NCAA doubles championships.

He won the NCAA doubles championship again in 1956, this time partnering Peruvian player Alex Olmedo.

At the 1958 Wimbledon Championships, he partnered with Rosie Reyes to make the semifinals of the mixed doubles.

In order to rest players, he featured in two dead rubber singles matches, against Yugoslavia and India, en route to the final.