WASHINGTON - British boxer Amir Khan, eager to avenge a controversial loss to Lamont Peterson, is already into the toughest training of his career for what he calls a must-win world title rematch in May.The 25-year-old Englishman will face Peterson on May 19 in Las Vegas for the International Boxing Federation and World Boxing Association light-welterweight titles after losing them to the American last December in Washington."I believe I won the first fight. I want those titles back," Khan said. "This fight means so much to me. It's going to be explosive."Saying he is already into his longest and most motivated training, Khan has already started workouts in England, plans to conduct high-altitude training in the Philippines and spend weeks at the Hollywood gym of trainer Freddie Roach. "I like the attitude," Roach said. "He has been training for a month already in England. Physically I think Lamont took more punishment last time. That's why I think we will have an easier time." Once a homeless youth on the streets of Washington, Peterson completed a fairytale with a split decision triumph over Khan marred by referee Joe Cooper taking a point from Khan in both the seventh and 12th rounds for pushing. Peterson, 28, won 113-112 on two judges' scorecards while the other had Khan a 115-110 winner. Without the deductions, Khan would have kept the titles."People still say I'm the champ," Khan said. "At no time has he said he won the first fight. It's all about how you come back from these fights and I always come back stronger. "There aren't that many British world champions out there and I'm going to be one again. I'm going to be ready for everything he brings to the table."Peterson, 30-1-1 with 15 knockouts, pondered other offers and was mentioned as a possible for Filipino star Manny Pacquiao but found fight fans wanted a rematch and that he still had something to prove against Khan."We had other offers that were interesting but everybody wanted to see a rematch," Peterson said. "On the street, on Twitter, comments I read, they really wanted that fight."I just want there to be no doubt I won that fight. I want to go out and prove I'm the better fighter. I will definitely leave no doubt come May 19."Khan, 26-2 with 18 knockouts, wants to forget controversies about Cooper's calls and the handling of the scorecards during and after the first fight."I haven't gotten to the bottom of it and I don't want to. I want to put it all behind me," Khan said. "I just want to win the next fight. I just want a fair fight and I promise 100 percent that I will win."Khan has other ideas than using his forearm and going to the ropes on how to deny Peterson position inside."His head kept coming in there. We're not going to be dealing with that problem now because I'm going to be hitting him," Khan said. "Now I know what to do and I'm not going to make the same mistakes. When he comes inside, instead of pushing him away, I can take a sidestep back.Roach is working on strategy adjustments after seeing more attacks than expected from Peterson."Lamont fought more aggressively than I have ever seen him fight before," Roach said. "Will he do that again? I'm not sure. If he does, we will have (Khan) ready to deal with that."Peterson, who says he suffered a bone fracture under his right eye from a Khan elbow in the first fight, plans to target Khan's midsection to weaken him for later rounds."Whether it's coming inside and throwing hooks or standing outside and throwing straight shots, I'm going to work on his body," Peterson promised.