Carl Froch clambered up from a shocking first-round knockdown to retain his WBA and IBF super-middleweight titles with a controversial ninth-round stoppage of George Groves in Manchester.
Froch was floored by a flinging right hand in the opening moments but clawed his way back into the bout and won a spectacular duel when referee Howard Foster jumped in to end the contest in the ninth.
Foster's intervention with Groves still on his feet sparked uproar, with both corner teams briefly squaring off in the ring while a crowd which had started off resolutely pro-Froch roundly cheered the challenger.
Questions were inevitably raised about the eagerness of Foster to end the fight which had rocked and rolled from one fighter to the other and produced some of the finest action seen in a British ring for some time.
Froch was staggered on his feet in a sensational sixth before retaliating with big shots of his own, and the ending when it came seemed premature but in Foster's favour Groves did appear to be offering little resistance.
Froch may have mocked Groves' credentials for sharing the same ring during the acrimonious big-fight build-up and appeared to believe he was due an easy and enjoyable night - but it proved anything but.
Despite Groves heading into the ring with an unbeaten 19-fight record, he had showed few signs of what was to come with arguably his best wins coming over his ex-amateur rival James DeGale and ageing Jamaican Glen Johnson at the end of last year.
But Groves had appeared unfazed by Froch's claims, even during a distinctly unusual build-up to the fight which saw him split with career-long trainer Adam Booth and instead put his faith in his former bag man Paddy Fitzpatrick.
Groves had revealed intricate details of how he planned to take the fight to Froch but it was clear from the outset he would also be up against the vast majority of the 20,000-capacity crowd who booed him to the ring.
Amazingly, Groves did almost exactly as he had promised, coming out crouched behind his jab and finding some early success.
The challenger took control of the centre of the ring and landed enough to redden the champion's nose in the early exchanges, and it became abundantly clear Froch was not going to have it all his own way.
What followed stunned the capacity crowd as Groves rammed home a right hand which floored Froch for only the second time in his career, before two more rights on the bell emphatically gave the challenger the first round.
Froch looked more settled at the start of the second but again appeared jolted by a pinpoint left hand from Groves before responding with his best shots of the bout so far, a pair of rights to the body which briefly stopped his opponent in his tracks.
Groves was making a mockery of many pre-fight predictions as he waded out for the third, connecting with two more sharp jabs and a cuffing left hook before the champion responded by landing a left and drawing the challenger in the kind of rugged exchange he preferred.
Groves withstood the assault and showed no signs of fading early in the fourth, once again taking to the front foot and stalking the champion, who showed the first signs of frustration when he was warned by referee Howard Foster for hitting on the break.
Froch edged a tighter fifth but waded right back into trouble in a furious sixth in which Groves clattered home swinging shots with both hands and almost had Froch out on his feet - yet a sensational round ended with Froch flinging back bombs and coming close to a knockdown himself.
After an inevitably quieter seventh, Froch started the eighth with two right hands and a serious warning from referee Foster for illegal use of his forearm, and another thrilling exchange once again brought the crowd to its feet.
The action came to a clattering and sudden end in the ninth when after a close-quarters exchange Groves appeared to turn his back and drop his hands, and as Froch poured in unanswered punches referee Foster quickly jumped in to end the contest.
Boos rang down from the capacity crowd when the verdict was announced, sealing a remarkable turnaround for brave Groves who exited to a hero's ovation.
Earlier, Scott Quigg made an explosive second defence of his WBA super-bantamweight title with a second-round stoppage over Argentina's Diego Silva.
The Bury 25-year-old decked his opponent twice with a vicious right hand leaving Silva flat on his back on the canvas and requiring medical attention.