Ukraine's Vasyl Lomachenko retained his super featherweight title with a seven round demolition of Nicholas Walters, whose corner threw in the towel in between rounds telling the referee "No mas".
But Walters denied quitting after the fight, telling reporters - "I didn't quit."
The two-time Olympic gold medal winner Lomachenko registered the biggest victory of his career in dynamic fashion as it was the second defense of his World Boxing Organization title and just his eighth professional fight.
"It wasn't about quitting," Walters said. "If you look at the last round, he caught me with some pretty good shots, and I was holding on just to survive the round. It would be stupid to come out after that last round."
He dominated the previously unbeaten Walters from the opening bell and was scoring at will by landing hard punches in the final round of the beatdown at the Cosmopolitan in Las Vegas.
Walters' face showed signs of the punishment he was taking in the ring, but it appeared that he could have continued if he chose to.
"Almost a year without fighting. I went up in weight," Walters said. "He was more active. So if you watch the fight you see he's been scoring more than I do. My good shots, they are not connecting. He's connecting more clearly than I am touching him. In the last round he started catching me more and more. He's a good fighter."
Lomachenko compiled an amateur record of 396-1 with Olympic gold medals in 2008 and 2012. He is now 7-1 as a professional.
Lomachenko captured his first world title in June of 2014, dominating former US Olympian Gary Russell to win his in his third pro bout. He matched Saensak Muangsurin's record for fewest fights needed to win a world championship.
The only blemish on his pro record was a loss to Mexico's Orlando Salido in Lomachenko's second professional fight -- when the vacant WBO featherweight title on the line.
It was an embarrassing first defeat for Walters as his decision to quit in the middle of the fight dropped his record to 26-1-1 with 21 knockouts.
Lomachenko said after the bout that he next wants to fight WBC super featherweight champion Francisco Vargas.