LAS VEGAS — Floyd Mayweather Jr. used his speed and accuracy to win a unanimous decision Saturday night over a game Miguel Cotto in one of his toughest fights ever. Mayweather dominated late, rocking Cotto in the 12th round to pull out a win and remain unbeaten in 43 fights. But it wasn’t easy, with Mayweather getting his nose bloodied and Cotto fighting until the final bell. Two judges scored the fight 117-111 and the third had it 118-110. The Associated Press had Mayweather winning 116-112. “You’re a hell of a champion,” Mayweather told Cotto in the ring afterward. “You’re the toughest guy I ever fought.” Fighting just a few weeks before he enters a county jail to serve a three-month sentence for domestic abuse, Mayweather found himself in a tough fight against a game opponent who never stopped moving forward. But he was faster and more accurate than Cotto and seemed to wear him down in the final rounds. In the last round, Mayweather landed his best punch of the night, a left uppercut that seemed to hurt Cotto. He followed that with several flurries to the head to wrap up a decision that until the later rounds had been in doubt. The decision was roundly booed by the crowd at the MGM Grand arena, which cheered wildly every time Cotto landed a punch. “He’s a tough competitor,” Mayweather said. “He came to fight, he didn’t just come to survive. I dug down and fought him back.” Mayweather, who was guaranteed $32 million, was forced to fight every minute of all 12 rounds against the Puerto Rican champion. He did it after weighing in at 151 pounds, the heaviest he has ever been for a fight.