After almost two decades of bickering, Kell Brook settled the debate inside six rounds.
The Sheffield star dominated Amir Khan from the first bell until referee Victor Loughlin stepped in to save the beaten man from further punishment.
Khan will surely now retire after a glittering career - and Brook would be wise to follow.
But the fight that should have happened five years ago was at least settled in decisive fashion in Manchester.
Despite the long wait, the demand was as intense as ever as the man from Bolton was cheered into the ring after the man from Sheffield had been roundly booed by the 20,000-strong crowd.
Manchester United's Edinson Cavani and City's Jack Grealish had nabbed tickets while Oasis legend Noel Gallagher also took a seat at ringside.
Brook had accused Khan of nit-picking for months over the negotiations with the rivals settling on a catchweight of 149lb which in theory suited Khan.
And debate continued to rage just minutes before the first bell with Brook forced to adjust his gloves in the ring.
Khan, dressed on white and gold, kept his back to Brook during the introductions.
The rivals did touch gloves, however, before Khan said one final prayer in his corner.
Khan looked to utilise his speed in the early stages but was caught with a jab coming in.
Then, after Khan had swung and missed with a hook, a shoot-out began which set the tone for the remaining rounds.
Book landed his first big shot of the fight as a right hand sent Khan back towards the ropes.
He tried to seize the initiative as Khan back-pedalled but the Bolton man was forced into throwing himself. That left him open and Brook staggered him again, this time with his left.
Khan’s speed and relentless movement at least kept him out of range but Brook was patient and landed a right hand in round two only for Khan to shrug it off.
The pace had slowed from a frenetic opening but Khan began to find the target - until Brook exploded into life in the dying seconds.
Khan appeared to be kept up by the ropes and then did hit the canvas but the referee ruled it a push.
Khan appeared to have recovered at the start of the fourth round but seemed unable to hurt Brook.
He did land a clean left hook but Brook showed little sign of distress before he again finished the round strongly to leave Khan clinging on.
It seemed only a matter of time before Khan wilted but his oft-criticised chin held up to another barrage in the fifth stanza.
But Book smelt blood at the start of the sixth - and this time he finished the job as the referee jumped into save Khan.
On the undercard, Natasha Jonas beat Christian Namus to become world champion at the third attempt.
Jonas had previously lost to the imperious Katie Taylor and drew with Terri Harper in her efforts to win honours.
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And she jumped up two weight divisions to take on Namus in Manchester for a vacant super-welterweight strap.
Olympic bronze medalist Frazer Clarke beat Jake Darnell in a first-round stoppage to kick-start what he hopes will be a successful assault on the heavyweight division.
Meanwhile, Viddal Riley, best known for coaching KSI to victory over Logan Paul in 2019, earned his fifth professional victory.
He dropped Willbeforce Shihepo in the first round but was unable to stop the veteran Namibian inside the six-round distance.
Nevertheless, Riley, 24, was awarded every round by the referee as he re-launched his career following four fights in almost as many years.
There were early stoppage wins for Brad Rea over Craig McCarthy and for Adam Azim over Jordan Ellison.
Adam's brother Hassan was made to work harder for the second win of his career as he was taken the distance by journeyman MJ Hall.
