Cruz was born in Taguatinga, Distrito Federal. The son of a steel worker, he began running as a 13-year-old, and showed great promise as a junior. At the age of 15 his personal best over 800 m stood at 1:51 min. After setting a junior world record of 1:44.3 min in 1981, he received a scholarship for the University of Oregon in 1983. The move immediately paid off, and Cruz won the National Collegiate Athletic Association (NCAA) championships over 800 m that same year. He also competed in the inaugural World Championships in 1983, winning the bronze.