Carl Frampton lost for the first time in his professional career as Leo Santa Cruz beat him on points in Las Vegas to regain the WBA featherweight title.
Mexico’s Santa Cruz, 28, got a deserved verdict in an all-action contest, and afterwards promised to fight Northern Ireland’s Frampton for a third time.
One judge scored it a draw, but the other two favoured Santa Cruz 115-113.
“Leo probably deserved it. It was my fault and I want to apologise to the travelling fans,” said Frampton, 29.
“I hope we can do it again – we need to do it again.”
Thousands of fans had travelled from Northern Ireland to help create a feverish atmosphere at the MGM Grand Garden Arena.
They saw Santa Cruz, a three-division champion, get off to a fine start, making better use of his height and reach advantage than he had when he lost to Frampton in July.
Frampton, who had won all 23 of his previous fights as a professional, warmed to his task more after a slow start.
But he found Santa Cruz, relentless with a productive jab, in determined mood to avenge that points defeat in Brooklyn.
Frampton won some rounds back and finished strongly in the 12th, but Santa Cruz held firm to take the belt.
“My feet were a bit slow. I needed to let my hands go a bit more when I got close,” added Belfast man Frampton.
“We had a fantastic training camp, I felt completely prepared. I feel like I’ve let the people down.”
Frampton said he would like Santa Cruz to come to Belfast for the third meeting between the pair.
And Santa Cruz said both he and Frampton ‘deserved’ a third fight.
He said: “He is a great fighter and a great counter-puncher.
“It was tough to change my style. In my head I wanted to go for it, but I was told to box him and that’s what I did.
“I am a man of my word. Let’s go again.”
Reaction – ‘Carl has the ability to beat him again’
Barry McGuigan, Frampton’s manager, on Sky Sports
These two young men are fantastic for boxing – they represent everything that is good about the sport. Carl emptied his tank, but didn’t fight technically as well as he could. It was a magnificent fight. I thought Leo deserved to win it.
I hope they will go back to Belfast, repaying these travelling fans for spending their hard-earned money. We owe it to them to bring it back to Belfast.
Shane McGuigan, Frampton’s trainer, on Sky Sports
No excuses, it was a nip-and-tuck fight. I think we will get Santa Cruz again, and I know Carl has the ability to beat him again.
We weren’t really expecting to box on the back foot, but we were a bit sluggish. He was a bit tired down the stretch but it is one of those things.
Analysis – ‘A non-stop, toe-to-toe, all-Mexican fight’
Former unified light-welterweight world champion Amir Khan
I think it’ll probably happen again. Both fighters fought a great fight, it was non-stop, toe-to-toe – an all-Mexican fight.
It was always going to be close because they have styles that suit each other. They’ve both got great boxing skills. One’s a fighter, one’s a boxer but then they have to change their skillset and gameplan a bit which makes it tough.
Santa Cruz was not the pressure fighter. He was the one who was moving back. He was the one who was boxing more, but in the first fight he was the one pushing Frampton back and you saw Frampton, in this fight, being more the pressure fighter.
The best man won but what a great fight it was.
Radio 5 live boxing correspondent Mike Costello
It was desperately close once again but Santa Cruz has won it on two judges’ scorecards. He’s come back and wrested his belt back. That’s the measure of a great champion. Everything about this suggests a trilogy.