Mikey Garcia suffered a shock points loss to Sandor Martin that severely dented the four-weight world champion's reputation.
The American star struggled with his timing from the opening bell as the Spaniard's sharp counter punches and clever movement were enough to secure a majority decision win with scores of 97-93, 97-93 and 95-95 in Fresno.
Garcia, who had been regarded as one of the top fighters in the US, slumped to his second defeat in three fights after his unbeaten record was ended by a points loss to Errol Spence Jr in 2019.
"I thought I was ahead on the three cards," Garcia told DAZN.
"It is what it is. That's why there's three judges. They decided he was the one winning the fight.
"He didn't beat me up, I'm not bruised up or anything.
"I knew he was a very good boxer. That's why I kept coming forward, but I knew I couldn't be reckless, either.
"I still thought I did enough to win. He kept moving around the ring.
"The judges this time thought he was in control. I thought I was in control."
Martin savoured a huge victory after making a sizeable step-up in class following a European title defence in his last fight.
"It's the biggest moment of my career," said Martin.
"I said all along that I was going to do it, and I did it."