Ocasio campaigned in the Heavyweight division, where he drew with Michael Dokes then lost by a knockout in the first round to the same boxer. Ocasio beat Jimmy Young by a 10 round decision to earn the right to challenge Larry Holmes for the world title. Attempting to become the first hispanic to win the world Heavyweight championship, Ocasio lost to Holmes by a knockout in seven rounds. He later went down in weight, to fight in the then newly created division of the Crusierweights, and in 1982 was matched with Robin Williams (the boxer) in South Africa for the vacant WBA title. Ocasio became a world champion by beating Williams by a 15 round unanimous decision. He shared honors as world champion of that division with countryman Carlos De Leon, the WBC world champion. Ocasio made three successful defenses, beating Young Joe Louis by a decision in 15 at Chicago, defeating Randy Stephens, once again by a decision in 15 at Las Vegas in 1983, and knocking out John Odhiambo in the 15th round at the Mario Morales coliseum (Then Mets Pavillion) in Guaynabo, Puerto Rico in 1984. He then returned to South Africa, where he lost his title to Piet Crous by a 15 round decision. One month after losing the title, his brother was murdered.
Ocasio, during his championship run, was able to buy a house in Trujillo Alto, Puerto Rico, where he mantained a large farm.
He also participated in a Puerto Rican movie, playing a slave in the production.
In 1986, he made a comeback, winning two fights, including a 10 round decision win in Aguadilla and another 10 round decision win, versus former world champion Dwight Muhammad Qawi in Atlantic City, before trying to regain his world championship against Evander Holyfield in Marseilles, France. He lost in his bid to recover the title by a knockout in 11 rounds.
Two more returns to South Africa resulted in a win and a loss versus a South African challenger who'd later fight 12 rounds versus George Foreman. After this, Ocasio called it quits. It is said that he resides in New York currently.
He retired from boxing with a record of 23 wins, 7 losses and 1 draw, with 11 knockout wins.