Juan Manuel Marquez of Mexico stopped Juan Diaz in the ninth round of a furious slugfest on Saturday to claim the American's IBO lightweight title along with the vacant WBA and WBO crowns.
Marquez, who was outworked by Diaz and felt his crunching left hooks early on, sliced through the American's defence with uppercuts from both hands to drop the local favourite twice in the ninth before the referee halted it at 2:40 of the round.
Marquez improved to 50-4-1, while Diaz dropped to 34-2. "He's a fighter that throws a lot of punches," Marquez said in the ring after the bout. "In the fourth and fifth rounds I was punching to the body and then the knockout came."
Diaz, 25, opened a cut over Marquez's right eye in the fifth round but the 35-year-old Mexican was already beginning to turn the tide in the fight.
Working more from the center of the ring than on the ropes where Diaz did his most damage, Marquez scored with vicious uppercuts and opened a gash over the title holder's right eye in the eighth round that covered his face with blood.
Marquez swarmed after Diaz in the ninth, unleashing combinations that set up more thudding uppercuts that finished off the American. "After I got cut, blood was in my eye and I couldn't do anything about it," Diaz said. "I couldn't see the punches Marquez was throwing.
"I kept fighting, fighting my heart out but he caught me with a good punch." Earlier, Chris John of Indonesia retained his WBA featherweight title by fighting Houston native Rocky Juarez to a draw.