Britain's Anthony Crolla was stopped in the fourth round by WBO and WBA lightweight champion Vasyl Lomachenko in Los Angeles.
Lomachenko, 31, defended his WBO and WBA lightweight titles, against heavy underdog Crolla, 32.
The fight was waved off after Crolla went down 58 seconds into the fourth round from Lomachenko's hard right hook.
Manchester-born Crolla was a heavy 100-1 underdog prior to the fight.
"Anthony's fine. Obviously it was a heavy knockout - a temple shot he didn't see," promoter Eddie Hearn told Sky Sports.
"After he was counted out he got up and was fine. But he's devastated. He said: 'I'm just so gutted for the team because of the work they did'. I'm like: 'Don't worry about the team, you just fought the pound-for-pound number one'.
"The third round was a weird one because he was sitting on the ropes. I thought it was a poor stoppage because although he wasn't particularly in the fight, it was a poor stoppage.
"Unfortunately in the fourth round Crolla knew he had to do something and go for it. When you do that against Lomachenko, you leave yourself wide open with gaps. Lomachenko was too good for Anthony.
"This shot came against the head; you can't not take this opportunity. Losing to Lomachenko is never a disgrace.
"He can have zero regrets because he prepared the best he could, it's just about levels. Who is going to beat Lomachenko?"
Two-time Olympic gold medallist Lomachenko improved to 13-1 with 10 knockouts.
The Ukrainian pound-for-pound champion scored the first knockdown of the night in the third round in front of a 10,000-strong crowd at Staples Center.
But Lomachenko dominated throughout, his right hook sending Crolla crashing to the canvas early in the fourth round.
Crolla dropped to 34-7-3 after a poor performance against overwhelming favourite Lomachenko - who called out his next opponent after the win: "I want Mikey Garcia. I want to unify titles. That's my goal. I want historic fights," Lomachenko said.
Before the fight, Crolla told BBC Radio 5 Live's boxing podcast that he wanted to "shock the world."
He faced criticism for taking the fight after the WBA and WBO world lightweight champion's original opponent - IBF champion Richard Commey - withdrew because of injury.