The October 7, 2006, trilogy fight between Diego Corrales and Joel Casamayor at Mandalay Bay presented immediate controversy before the opening bell. Corrales, weighing 139 pounds, forfeited his WBC and Ring Magazine lightweight titles on the scales, four pounds over the 135-pound limit. This weight miss cost him $240,000 in Nevada State Athletic Commission fines and required additional purse concessions from his $1.2 million earnings to salvage the bout.
The fight developed as a tactical affair. Casamayor established early control with strategic bodywork, taking rounds three and four with practical left hands and clinch work that drew referee Kenny Bayless's warnings. Round five featured a disputed knockdown call against Casamayor, ruled by Bayless despite clear replay evidence showing a trip.
Mid-fight action swung between both fighters, with Corrales testing Casamayor's chin after a low blow break in round eight. A sixth-round head clash cut Corrales near his left eye, while the final round saw Corrales bloody Casamayor's nose. The late rounds proved decisive, with judges Jerry Roth (114-113 Corrales), Nobuaki Uratani (115-112 Casamayor), and Adalaide Byrd (116-111 Casamayor) splitting their cards. The Associated Press scored it 116-112 for Casamayor.
This bout marked Corrales's final collaboration with trainer Joe Goossen, ending in a lawsuit over purse percentages—Goossen claimed he received $10,000 instead of the agreed-upon $120,000. The trilogy concluded with Casamayor winning their rivalry 2-1 and claiming the vacant titles in their final meeting.