Manny Pacquiao lost his WBO welterweight title to Timothy Bradley after a highly controversial split points decision in Las Vegas.
Despite landing 94 more punches during the fight, the Filipino was beaten for the first time in seven years after two judges scored the bout 115-113 in the undefeated American's favour.
The other judge at the MGM Grand had Pacquiao ahead by the same margin.
The decision was roundly booed and a rematch looks likely later this year.
Pacquiao tried to turn the fight into a brawl, using his power to hurt Bradley in the early rounds, but the Californian changed tactics in the middle rounds and it proved decisive.
"I thought I won," Bradley said. "I didn't think he was as good as everyone says he was. I didn't feel his power."
He displayed his confidence by having oversized tickets printed for a rematch on 10 November.
Despite landing some big shots in the fourth and fifth rounds, Pacquiao struggled to land any decisive blows thereafter but seemed to have done enough to retain his title.
"Can you believe that? Unbelievable," promoter Bob Arum said. "I went over to Bradley before the decision and he said, 'I tried hard but I couldn't beat the guy.'"
Pacquiao said he was shocked by the verdict: "I did my best (but) I guess my best wasn't good enough.
"He never hurt me with his punches, most of them landed on my arms," Pacquiao said.
Arum, who has contracts with both fighters, said: "I'm going to make a lot of money on the rematch, but this [decision] was outrageous."