Las Vegas: Mexican professional boxer Saul 'Canelo' Alvarez knocked out Britain's Amir Khan in the sixth round in Las Vegas to retain his WBC middleweight title. Until the brutal ending, Khan had used his superior speed and movement to frustrate the champion and appeared to be well ahead on points. However, when Khan lost concentration for a split second, the champion knocked him out cold with a huge right hander, the BBC reported on Saturday. Khan, 29, jumped two weight divisions to challenge Alvarez and was attempting to become only the third former light-welterweight world champion to win a middleweight world title. Khan probably edged a cagey first round courtesy of a couple of flurries and one well-aimed right cross, although Alvarez did land with a flashing left hook. Khan repeatedly made the champion look clumsy in round two, landing with rapier-like combinations before darting out of range. And when Alvarez landed with a juddering left hook, Khan stood up to it and returned fire. It was more of the same in the third, with Alvarez, 25, stalking his prey and finding himself confounded by Khan's blinding hand-speed and volume of punches. At this stage, Khan's prediction that speed and movement would trump power looked like it might come true -- he was certainly confounding those critics who said a year of inactivity would blunt his edge. Khan unleashed more flashy combinations in the fourth and while none of his punches appeared to be hurting Alvarez, the Englishman appeared to be well ahead on points a third of the way through the contest. There were signs in the fifth that Alvarez was beginning to find his range and at the start of the sixth he connected with a hurtful left-right combination. And when Khan left his left hand dangling soon after, Alvarez exploded an overhand right on his chin, rendering him unconscious before he hit the canvas. Khan was counted out with 23 seconds remaining in the round. Khan later congratulated Alvarez on his Twitter account. "I am okay everyone, that's boxing for you. Congrats to Canelo monster punch. Much love to all the fans," he tweeted.