Cruz was highly successful as a junior athlete. He won three straight golds at the Central American and Caribbean Junior Championships in Athletics, winning his first at the age of fourteen in 1986 and his last in 1990. He became world junior champion in 1988 and returned two years later to defend his title, narrowly finishing second behind Ilya Markov (who would go on to win an Olympic medal in the sport). Cruz also won two consecutive gold medals at the Pan American Junior Athletics Championships (1989 and 1991).