Gennady Golovkin suffered the first loss of his professional career after Saul 'Canelo' Alvares clinched their middleweight world title fight in Las Vegas on Saturday.
A year after their first fight ended in a controversial draw, Alvares survived a late barrage from Golovkin to clinch a points decision in front of a frenzied capacity crowd at T-Mobile Arena.
Two judges scored it 115-113 for Alvares, while the other had it a 114-114 draw.
Golovkin landed some huge head shots in the closing rounds, opening a big cut above Alvares' left eye, but the Mexican held on to improve his career record to 50-1-2, including 34 knockouts.
Golovkin fell to 38-1-1, with 34 knockouts.
"It was a very tight fight," said Alvares in a ringside interview after becoming the WBC, WBA, IBO and Ring Magazine world champion.
"I looked for a knockout but it's difficult. He's a great fighter but in the end I got the victory.
"I'm very excited, very emotional. I want to thank everyone who believes in me. This is for them and long live Mexico."
Kazakh Golovkin, 36, was tentative early but clearly aware he was behind on points got more aggressive as the fight progressed.
But Alvares landed more body punches, 46-6 by the official count, and more power punches, even as Golovkin landed more overall punches.