Sandoval's next fight was held on 15 March 1984. Despite his record of 22 victories without any losses, including fifteen knockouts, he was a virtual unknown to most boxing fans when he met the Lineal and WBA Bantamweight champion Jeff Chandler in Atlantic City. After dropping the champion in round eleven, Sandoval won by TKO in round fifteen to become a world champion in a major upset. He followed this up with his first trip abroad as a professional boxer, to Monte Carlo on September 22. He outpointed the top ranked and well known Edgar Román over fifteen rounds on the undercard of Donald Curry's sixth-round knockout win over Nino LaRocca. He fought again on 15 December against Cardenio Ulloa, who was attempting to become the first Chilean world boxing champion in history. According to the report made by "Ring En Español", Ulloa caused Chilean dictator Augusto Pinochet to jump off his chair with excitement when he dropped Sandoval in the third round, but Sandoval recovered and retained the title with an eighth-round knockout.