Tony Bellew said he feared for David Haye's safety and asked the heavyweight and his corner to end Saturday's fight at the O2 Arena before he scored an 11th-round stoppage.
Haye, 36, damaged his Achilles and was put down in the sixth round but gamely carried on and went for surgery on the injury after the bout.
"Just before the stoppage I looked at David and said 'stop now'," said Bellew. "He shook his head.
"He went beyond the call of duty."
The Liverpudlian added: "I looked at Shane McGuigan (Haye's trainer) and said 'stop it'. I was worried as he couldn't box."
The two fighters had engaged in a controversial war of words ahead of the fight but afterwards Bellew spoke of Haye's bravery in refusing to give up.
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"In rounds four and five he was tired but he was blocking, when we got to nine, I felt myself on top of him and I could feel him panicking," said Bellew.
"I said, 'stop, stop' and he went 'no'. He gets a lot of admiration from me from a sportsman's perspective."
Haye - who notably lost his ability to move freely after stumbling in the sixth - was unable to attend a post-fight news conference as he was on his way for surgery on an injury for which he reportedly flew to Germany for treatment during fight week.
But in the ring he told BBC Radio 5 live the injury was "just one of those things" and conceded "the better man won".
'I've grown to hate the circus'
Bellew, who was visibly emotional early on in his news conference, said he thanked Haye in the ring for "helping secure my kids' future".
The WBC cruiserweight champion, 34, defied most pre-fight predictions to win on his heavyweight bow but told reporters this would be his final 12 months as a fighter.
"There's a certain number of times you can keep doing this and it's not many more times I'll be honest," added Bellew, who now has 29 wins and a draw from 32 fights.
"This circus is going to keep following me now. I don't actually like all this, I've grown to hate it. I'm not a perfect person, I make bad moves and bad mistakes in my life, I just want to be left alone now and enjoy time with my kids."
His trainer Dave Coldwell added: "I would be happy if he walked away. He won a world title, he secured his family's future, so for me, I would be happy if he said 'that's us done'."
'A shot at heavyweight glory'
Bellew labelled boxing a "freak show" in which he was happy to play the "pantomime" but when asked why he would not bow out now, he said any offer for his next fight "would be too big" to turn down.
Promoter Eddie Hearn believes Bellew's future lies in the heavyweight division, with title-shots makeable against American WBC champion Deontay Wilder or New Zealand's Joseph Parker, who holds the WBO belt.
Hearn said: "Everybody was saying David Haye is one of the best heavyweights in the world. So as far as I'm concerned Tony's earned his shot at the heavyweight title of the world.David Haye fell through the ropes when he was put down for a second time in the 11th round
"I could bring Wilder or Parker to the UK without any shadow of a doubt."
A rematch with Haye was briefly mentioned in the ring but Hearn appeared cold at the prospect, stating the former WBA heavyweight champion's camp had no desire to insert a rematch clause before the bout.
Bellew added: "The biggest one-punching heavyweight in the world couldn't put a dent in me. There's a new sheriff in town."
A message for the board
Bellew was moved to tears when explaining a video chat with his son before the fight where he was urged to "come home safe".
Controversial comments from both fighters, including Haye's graphic descriptions of the harm he hoped to cause his rival, had marred fight week.
The British Boxing Board of Control (BBBofC) will discuss the acrimonious build-up next week.
"What we have done for boxing tonight is put it on a pedestal," said Bellew. "Two men fought their hearts out."
He called the BBBofC's proposed meeting "a disgrace", adding: "The board can't say nothing to me and if they do, I will go and get a license somewhere else. The cheek of it."