Nieves represented his native country at the 1996 Summer Olympics in Atlanta, Georgia. He was the bronze medallist at the 1998 Ibero-American Championships in Athletics. He was the 2003 gold medallist in the steeplechase at the South American Championships in Athletics.
He won the gold medal in the men"s 3000 metres steeplechase event at the 2003 Pan American Games in Santo Domingo, Dominican Republic. Regionally, he won medals at the South American Games, Central American and Caribbean Games, Bolivarian Games and the Central American and Caribbean Championships in Athletics. He was highly success at regional age category competitions, with a highlight being a triple gold medal win at the 1990 Central American and Caribbean Junior Championships in Athletics, which included a championship record in the 2000 metres steeplechase.
