The fight, in front of a sellout, celebrity-studded crowd that included Mike Tyson, actor Will Smith and basketballer LeBron James at T-Mobile Arena, lived up to its billing as the best two pound-for-pound fighters in the world.
Alvarez claimed a majority decision, with the judges' scorecards reading 114-114 115-113 115-113.
The fight came after an acrimonious weigh-in during which Alvares nearly head-butted Golovkin, who is known affectionately through the boxing world as "Triple-G".
He took control with a dominant spell in the middle rounds before holding off Golovkin down the stretch to claim a 114-114, 115-113, 115-113 win. I am a great fighter, and I showed it tonight.
The match was among the most anticipated, if not the most anticipated, fights of the year after their initial encounter ended up rather unconvincingly. I thought it was a very good fight for the fans, and very exciting. At times their heads were nearly touching, bringing hooks and uppercuts into focus, with Alvarez landing a well-placed right to the body in the sixth.
Alvarez (50-1-2, 34 KOs), who is now the WBA, WBC and IBO middleweight champion, dealt Golovkin his first loss after going undefeated in his last 39 fights, including a split draw against Alvarez in their first bout a year ago.
"There's no doubt about it. Golovkin won the fight", Atlas said.
"I think he's scared". The rematch had originally been scheduled for May 5 but a failed drug test, which Canelo blamed on tainted meat he had consumed, delayed it four months.
"If the people want us to do it again let's do it again, " Alvarez said.
'You can either fight as going inside and imposing your body on the other guy, or you fight on the outside and use the jab, control the range and make the smaller guy take all the chances.
"It was very hard and [Golovkin] is a great fighter". He was the one who was backing up. He's a great fighter but in the end I got the victory. "It was a clear victory". "Hopefully there'll be a third fight".
Perhaps Alvarez's best trick in the rematch came in the second half of the fight when he absorbed a number of clean strikes from Golovkin that have previously removed the ghost from a series of opponents before him, including an incredible 23-fight knockout streak between 2008-17.
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