On May 7, 2005, Corrales defeated WBC and Ring Lightweight champion José Luis Castillo via TKO in the tenth round, giving Corrales his fourth title in 2 weight classes. The fight is almost universally regarded as the best fight of 2005. Both men stood in front of each other, battering each other with hard combinations and power punches throughout the entire fight. Finally, in the tenth round, Castillo knocked Corrales down. Seconds later, Castillo knocked Corrales down again. Once on the ground, Corrales managed to beat the count, and, after a point was taken away for excessive spitting out of the mouthpiece, Corrales connected with a punch that Castillo later called "a perfect right hand." Corrales then trapped Castillo against the ropes and landed numerous punches, causing the referee, Tony Weeks, to stop the fight.