Mosley vs Leija, Johnson

On November 14, 1998, Mosley faced his toughest defense to date when he fought 32 year old former WB super featherwight champion Jesse James Leija (37-3-2, 15 KOs) at the Foxwoods Resort in Mashantucket, Connectiut. This was Mosley's sixth defense of his IBF world title. As the fight progressed, Leija ws knocked down in rounds 6,7 and 9. The fight was stopped when Leija couldn't answer the bell for round 10, rewarding Mosley with a deserved victory. Mosley was leading by scores of 89-78, 89-78 and 88-79 at the time of the stoppage. Leija took the fight with 3 weeks notice.

Mosley took only two months off returning to the ring to defend his title in January 1999 against American Golden Johnson (15-2-2, 10 KOs) at the Civic Center in Pensacola, Florida. The fight ended when Mosley connected Johnson with a flurry of punches as he was against the ropes and then dropped to both knees. He beat the count, but was put down again seconds later, ending the fight.

On April 17, 1999, Mosley made his 8th and final defense of the IBF lightweight title against former USBA super featherweight champion John Brown (19-5, 10 KOs) at the Fantasy Springs Casino in Indio, California. The fight was stopped after round 8 when the ringside doctor intervened. Mosley won the fight via TKO to retain his title.

Welterweight

Mosley vacated his lightweight title and moved up two weight divisions to welterweight, scored two consecutive knockouts against Wilfredo Rivera and Willy Wise, setting up a huge fight against Oscar De La Hoya for the WBC welterweight title.

Mosley vs Diaz, Taylor

Mosley defended his newly won titles on November 11, 2000 at the Madison Square Garden theater in New York against Mexican boxer Antonio Diaz (35-2, 24 KOs). The fight lasted six rounds, after Mosley knocked Diaz down twice. Diaz was also down once in round 2.

On March 10, 2001, Mosley was scheduled to fight unbeaten Australian Shannan Taylor (28-0-1, 18 KOs) at Caesars Palace in Las Vegas. Shannan was knocked down once in the first round. He was losing all rounds, up until the end of the fifth round. Taylor lost the fight when he decided not to return for round 6.

Mosley vs Stone

On July 21, 2001 Mosley easily beat IBO World super welterweight champion Adrian stone (30-3-2, 23 KOs) knocking him out in round 3. The fight took place at Caesars Palace in Las Vegas. Stone moved down to welterweight for the first time in three years to challenge Mosley and was losing the first two rounds before being stopped. Following the win, Mosley said he would like to have a rematch with De La Hoya in a split 50/50 fight or a unification fight against unbeaten Vernon Forrest.

Mosley vs Forrest I, II

It was finally announced that Mosley would be defending his WBC and Lineal welterweight titles against Vernon Forrest (33-0, 26 KOs). The fight took place at the Madison square Garden theater in New York City on January 26, 2002. The ring Magazine welterweight title was also at stake. Mosley was knocked down twice in the second round as he went on to lose a unanimous decision, his first loss in his professional career. In round 2, Mosley suffered a cut at the hairline from an accidental clash of heads. The final scorecards read 115-110, 117-108 and 118-108 all in favor of Forrest.

Mosley and Forrest met in an immediate rematch on July 20, 2002, at the Conseco Fieldhouse in Indianapolis. Forrest being the 'A; side, received $3.42 million compared to Mosley's $2.8 million. The fight was also known at the time for its attendance of 15,775 which was the largest boxing crowd ever in Indiana. The fight went the full 12 round distance. The scorecards were closer than the first fight, however still had Forrest as the winner (117-111, 116-112, 115-113) unanimously. USA Today scored it 115-113 in favor of Forrest. Forrest kept on the outside using his height and reach as an advantage.