In April 2012, Castillo signed for the
boxing promoter Acquinity Sports along with compatriots
Manuel Félix Díaz and
Argenis Mendez. One month later, in May he won by
unanimous decision to the Mexican Alvaro Enriquez to improve his record to (5-0-0) in a fight held at the
Seminole Hard Rock Hotel and Casino in
Hollywood, Florida, United States. In July, he knocked out the
Mexican Ricardo Campillo in the second round in a Light Heavyweight category combat held in Hollywood, Florida, improving his record to 7-0. In Santo Domingo, in October, he knocked out compatriot Emilio Cayetano who did not come out for the 5th round, resulting in the fifth TKO and eighth victory for Castillo. After compiling a record of 15-0-1, Castillo suffered his first professional defeat to Joseph Williams, who won their fight by a majority decision. After fighting six more times, with a record of 5-1 (the loss coming to
Marcus Browne), Castillo challenged
Dmitry Bivol for his
WBA (Super) light-heavyweight title on October 12, 2019. He lost by a unanimous decision. On September 25, 2021, Castillo suffered a brutal knockout loss to
Callum Smith, on the undercard of
Anthony Joshua’s world heavyweight title defence against Oleksandr Usyk. He hit the canvas after taking a right hook to the chin from Smith and his legs began to shake uncontrollably. He was hospitalised after suffering a seizure, but was later released. ==References==