Amir Khan was knocked out inside six rounds as his brave title challenge in his David v Goliath clash with Canelo came to an abrupt end.
Khan fought well and had edged the first five rounds on most observers' scorecards as he hit and moved.
But Canelo caught up with him in the sixth and connected with a couple of shots before delivering his devastating one-punch KO.
He caught Khan flush on the left side of his jaw and the challenger was out before he hit the canvas.
Khan lay flat on his back with his arms by his side - in shades of and referee Kenny Bayless waved it off without even bothering to start counting.
Khan was eventually helped from the ring and he deserves huge credit for his brave challenge.
After taking a couple of minutes to gather his senses, Khan, confirmed he will move back down to welterweight.
I'm one of those fighters who will step in the ring with whoever," he said.
"I showed my balls by getting in the ring with a big guy. This is boxing. I wanted to get in there. I didn't make it to the end, but I tried my best. I'd like to thank all my fans for supporting me.
"I want to be best and fight the best. This is why I accepted this challenge. I'll probably go down. My natural weight is 147. I'll probably go down to that after this."
Canelo, who claimed he would now face Gennady Golovkin, who was ringside, said: "I knew he was very fast.
"I knew it would be like that, but in the latter rounds it would come to my favour."
The fight marked Khan's return to the big time after four years trying to regain a seat at boxing's top table after being sparked out by Danny Garcia.
It has been a long road back and Khan revelled in being back in the limelight in the first fight at the new T-Mobile Arena.
It was unfamiliar territory for Khan and he was a huge underdog with the bookies, while most fans among the crowd were cheering for Canelo.
Khan began well and landed a swift left-right combination to show Canelo that he had not lost any of his hand speed by stepping up two divisions to middleweight.
The bigger Canelo was all about power and he caught Khan with a clubbing left hook to give him an early taste.
Khan was also light on his feet and he countered with another left-right combination in the second round after Canelo swung and missed.
Canelo tried to close the distance to Khan and caught him with a left hook in the third. The champion was slowly working his way into the fight.
Khan continued to buzz Canelo with his faster hands, but Canelo managed to counter one foray with a right hook to the body.
Canelo began to land in the fifth and rocked Khan with a left hook to the head and then a right hook to the body.
The Mexican had found his range and knocked Khan's head back with a three-punch combination in the sixth, although the Bolton fighter gamely replied with his own combination.
That was a worrying sign of what was to come and 30 seconds before the end of the round, Khan floored Khan with a single right to the side of his left side of his jaw.
Khan lay flat on his back as referee Kenny Bayless waved the fight off.
