Amir Khan's (33-5) WBO world welterweight title fight with Terence Crawford (35-0) ended in bizarre fashion when he was pulled out by his corner following a low blow.
The Briton was decked in the opening round and then received an accidental punch to his groin in the sixth. After consulting his corner, consisting of trainer Virgil Hunter, they decided to withdraw from the contest citing that he was in "too much" pain.
The unbeaten American champion was dominant throughout the contest and leading on all three scorecards, and later questioned whether Khan quit, urging the him to "tell the truth".
"I would never quit, I would rather get knocked out," Khan, 32, responded.
"I have never been hit below the belt and was in pain.
"I want to apologise to all of the fans. The fight was just getting interesting."
Boos rang out at New York's Madison Square Garden post-fight and rival Kell Brook has been quick to publicly criticise his arch-enemy.
Former world middleweight champion Andy Lee added that Khan had "done himself a misservice", while former two-weight world champion Paulie Malignaggi said he "wasn't going to get back into the fight".
Already a heavy underdog against the three weight divisional champ, Khan looked apprehensive during his ring walk and a right hand staggered him in round one, sending him to the canvas.
He was unable to cope with the superior skills of the champion and absorbed some hard body shots in the fourth segment, only landing on rare occasions of his own.
When Crawford, 31, drove a left hook into his groin in the sixth stanza, Khan was legally allowed to take five minutes to recover but, after about a minute, the bell sounded.
"I could feel it in my stomach and legs. I said 'I can't move'," Khan explained. "There was no point taking five minutes out, I could not continue. I am not one to give up. I was hit by a hard shot below the belt.
"I couldn't continue as the pain was too much."
When an accidental injury ends a bout in which four rounds have been contested, the judges' cards are used, but the announcement of a technical knockout meant Khan was stopped.
Crawford was leading 49-45 50-44 49-45 on the cards at the time of the stoppage.
There was brief confusion as to whether he might have been disqualified but upon being declared the victor he immediately said he hoped to face IBF champion Errol Spence Jr next.
In the post-fight news conference Khan was responding to claims he had done so when Crawford interrupted by asking: "Did you quit? Tell the truth".
Malignaggi added: "It was on its way to being a stoppage. That's probably the best way for Amir to leave the ring because it means he's not going to take any more punishment. He wasn't going to get back into the fight. Khan just needed a moment to be done. That was his moment."
Khan's trainer Virgil Hunter told BBC Radio 5 Live: "The crowd will always be bloodthirsty and want to see a dramatic ending but you have to look out for the safety of the fighter. He's not the kind of fighter to make things up. I believe he was incapacitated.
"We knew we were behind but Amir was starting to work things out and pick up his rhythm."
The Bolton boxer has already said he will come back for another fight and that he is not done yet.