After his win versus De La Hoya, Mosley was considered the world's best fighter by boxing magazines. But he then ran a successful string of defenses against lower opposition such as Adrian Stone, and lost twice to Vernon Forrest, both times for the world title he had won against De La Hoya.
On February 8 of 2003, Mosley's bout with former IBF world Jr. Middleweight champion Raul Marquez ended in a no contest when Mosley accidentally head butted Marquez twice in round three.
He and De La Hoya faced each other for the second time on September 13, this time with De La Hoya's WBC and WBA world Jr. Middleweight belts on the line. Mosley defeated De La Hoya by a 12 round unanimous decision, and joined the exclusive group of world boxing champions that have reigned in three or more divisions.
On January 9, 2004, news ran across that the FBI was involved in an investigation into the De La Hoya rematch. According to the news, the fight's judges that night might have been bribed by outside forces to score the fight for Mosley, something Mosley and his handlers might not have been aware of.
Mosley currently holds a record of 39 wins, 2 losses and 1 no contest, with 35 knockouts.