"He came to fight, he didn't just come to survive. I dug down and fought him back," said the man considered as boxing's biggest villain at the moment.
Mayweather found himself in a war for the first time in his career after a long while, although he did display tremendous speed and landed more accurate punches.
But Cotto came moving forward and scored a number of heavy blows, including a lethal double jab that left the unbeaten fighter with a bloody nose in the sixth round.
Cotto appeared to have gained momentum after that as he relentlessly pursued Mayweather around the ring, eventually catching him up with several big shots in the eighth that had the crowd up on its feet by the end of the round.
But the Puerto Rican appeared to have tired going in to the final few rounds, allowing Mayweather to dominate again.
In the 12th, Mayweather rocked Cotto with a perfect left uppercut inside the final minute, forcing the Puerto Rican to briefly clinch and escape going down.
"You're a hell of a champion," Mayweather called out on Cotto shortly after the decision was announced. "You're the toughest guy I ever fought."
Cotto lost for the first time since suffering a 12th round technical knockout to Filipino boxing superstar Manny Pacquiao in a 2009 welterweight title fight. He fell to 37-3, with 30 KOs, and earned $8 million.
"The judges said I lost the fight and I can’t do anything else," said the Puerto Rican, who had a welt just below his left eye. "I did my best tonight." (GMA News)