Ryan Garcia suffered the first defeat of his career as Gervonta Davis delivered a devastating seventh-round knockout in Las Vegas on Saturday.
American Garcia was hoping to extend his record to 24-0 in the non-title 136lb (9st 9lb) catchweight fight.
However, the 24-year-old was counted out after compatriot Davis landed a short left counterpunch to his ribcage.
"I am the face of boxing," said 28-year-old Davis, who now has 27 knockouts in 29 unbeaten fights.
Davis suggested that his win was as big an event as pop star Rihanna's half-time performance at February's Super Bowl.
He said: "I just saw Rihanna perform at the Super Bowl and I was like that was going to be me one day, and here we are."
Garcia, who is yet to earn a top-flight world title, said it was "an honour" to be in the ring with Davis, who has won five world titles in three weight classes.
"I just couldn't recover. Snuck under me and caught me good," Garcia said.
"I was going to get back up, but I just couldn't get up."