By Ryan Burton

Canelo Alvarez got on his knees to check on Amir Khan after knocking him unconscious with a big right hand in the sixth round of their title fight.

Then he went over to check on some future business with fellow middleweight champion Gennady Golovkin, who was watching ringside.

It's a fight both Golovkin and boxing fans have been waiting for to happen, though the weight could be an issue. Alvarez wants the bout to be less than the 160-pound middleweight limit, while Golovkin, who holds his own piece of the middleweight crown, vows to fight at his best weight.

Against Khan, Alvarez needed only one big right hand to turn a close fight into a smashing knockout that left the British challenger out cold on his back in the middle of the ring.

Struggling with Khan's speed, Alvarez unleashed a long right hand that sent Khan backwards on the canvas, where referee Kenny Bayless didn't even bother to count him out at 2:37 of the sixth round.

Alvarez retained his piece of the middleweight title, but it was not without some nervous moments for his fans who packed the new T-Mobile Arena on the Las Vegas Strip. Khan was more than holding his own in a tactical fight when the right hand suddenly ended it.

Khan, a 6-1 underdog, had vowed to use his speed to confound Alvarez and his plan seemed to be working. He fought in spurts, landing combinations and seemingly frustrating Alvarez with his movement.

But a right hand that came out of nowhere landed flush against Khan's chin, and he was out before he hit the canvas.

Khan was taken to the hospital after the fight, but promoter Oscar De La Hoya said he appeared to be fine and that the move was precautionary. Khan's head snapped back when he hit the canvas and he appeared out for several minutes before regaining consciousness.

Alvarez was making the first defence of the WBC title he won from Miguel Cotto in November, though the fight was fought at a catch weight of 155 pounds. The WBC has said it will take the tile from Alvarez if he does not begin talks for a fight with Golovkin within 15 days.