After winning a preparatory fight, Dieppa would fight against Andy Tabanas for the vacant WBO championship. The fight was organized at the Madison Square Garden in New York City. Dieppa won the fight by knockout in the eleventh round. His first title defense took place on September 29, 2001, where he retained his title with a twelve-round unanimous decision over Fahran Sakkreehrin. The end of the fight with Sakkreehin marked the beginning of Dieppa's managerial problems. During this timeframe Félix Trinidad Sr. retired, leaving Dieppa without a trainer. As a consequence Dieppa spent several months inactive. His next fight took place on August 24, 2002, against John Molina. Defending his WBO Jr. Flyweight title for the second time, Dieppa suffered an injury product of accidental headbutt in the second round, which led to the fight being declared a technical draw.