Ricardo Mayorga twice knocked down Fernando Vargas to seal a majority decision in Friday's grudge non-title super-middleweight contest.
Nicaragua's Mayorga floored his fellow former world champion in the first and 11th rounds and went on to win with scores of 115-111, 114-112 and 113-113.
"In training I showed a lot more discipline and I was able to put it into practice," said the 34-year-old.
Vargas, 29, confirmed that the Los Angeles fight would be his last.
"This is my last fight. You don't want to have a bad night but sometimes it's just one of those nights," he said. "He was the better man."
The build up to the bout had been acrimonious, with the fighters consistently bad mouthing each other following a brawl between the pair when the fight was announced.
"It was a difficult thing to overcome the de la Hoya loss but I was able to come back with a big win"
Mayorga started the stronger at the Staples Center and put Vargas on the canvas with a right uppercut at the end of the first round.
Vargas wobbled again in the next before slowly coming into the fight, only for Mayorga to dominate again as the contest drew to a close.
And Mayorga claimed his decisive second knockdown late in the 11th round when he smashed a right into the face of his opponent.
Vargas was kept on the defensive for much of the 12th round and Mayorga even had time to raise a hand in victory between exchanges.
American Vargas, 29, admitted Mayorga's focus and discipline had surprised him but added: "I don't want to take anything from Ricardo. He just got the better of me."
Three-time world champion Mayorga, who last won 27 months ago, improved to 29-6-1 with a win in his first fight since losing the WBC light-middleweight title to Oscar de la Hoya 18 months ago.
"It was a difficult thing to overcome the de la Hoya loss but I was able to come back with a big win," he said.
"The style of fighting he came with, I didn't anticipate it, but I was able to change and come up with it."
Cintron said he broke his hand on the first punch he landed at the start of the fight but did not show any signs of pain until moments after a flurry that prompted referee Jon Schorle to halt the fight 1:53 into the 10th round.
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