Mexico's Antonio Margarito stopped Miguel Cotto of Puerto Rico in the 11th round to win the WBA welterweight title on Saturday.
Margarito (36-5, 27 KOs) knocked Cotto to his knees with a flurry of hard punches midway through the round.
Cotto, who beat the count but was clearly badly hurt, survived a follow-up barrage of punches, but as Margarito moved in again, the Puerto Rican sunk to his knees, prompting his corner to throw in the towel.
Cotto (32-1, 26 KOs) outboxed Margarito, a former WBO and IBF champion, for the first half of the scheduled 12-round bout, landing combinations and then moving out of range.
He frequently stood with his back to the ropes, luring Margarito in and responding with sharp counter punches.
Cotto also proved adept at slipping Margarito's blows, and at the end of the fifth round he stood with his hands down, moving his head calmly and causing his opponent to miss.
However, Margarito pressed forward relentlessly and in the seventh round, he landed several uppercuts that staggered Cotto and caused blood to gush from his nose.
Much of the sting then seemed to evaporate from Cotto's punches and Margarito seized the initiative.
"Obviously, Cotto is a very strong fighter," Margarito told reporters. "I told my corner during the fight that I would knock him out and I did.
"He never hurt me. That was the game plan, to come out early and strong and knock him out. I got him with body shots, then I hit him in the head, and I knocked him out."
Cotto praised his opponent afterwards.
"I'm very proud and very happy I was able to give the fans a great fight," he said. "Life continues. It isn't over. I'm going to take a long break and decide what I'm going to do next.
"This was Margarito's night. He's an excellent fighter and he did his job better than I did mine."