In 2013, AIBA revised its rules by eliminating protective gear and decided to raise the age limit for participants in the elite category to 19 years old, leaving the 17-year-old Santiago with the only option of participating in junior tournaments or risking injury by fighting without headgear under the new rules.[3] Having already competed in nearly 200 amateur fights, he decided to begin a professional career.[4] However, his residence complicated this move, because the Pennsylvania State Athletic Commission does not allow anyone under the age of 18 to turn professional.[5] After taking under consideration the circumstances and reviewing his amateur performance, the entity made an exemption and granted Santiago a license, making him the youngest professional boxer in the history of the state. He headlined his first event, defeating Moses Molina by knockout in the first round.[6] Santiago repeated this performance two weeks later in a win over Christian Daniels.[7] His next fight was against William Lorenzo, concluding in his first unanimous decision win. On April 5, 2014, Santiago made his professional debut in Puerto Rico, knocking Luis Ortiz Medina by knockout in the first round.[8] His next fight against Josh Beeman marked the first time that he competed in a six-round fight. During this timeframe, Santiago was signed by adviser Al Haymon.[9] The following month, he defeated Josh Beeman by unanimous decision in his first six-round fight.[10] On June 19, 2014, Santiago returned to Puerto Rico and outscored Carlos López in the undercard of a McWilliams Arroyo card.