Josh Warrington rose to the occasion on Saturday with an inspired performance to upset the odds and end Lee Selby's reign.
Warrington captured the IBF world featherweight title by split decision scores of 116-112 and 115-113 to 115-113 in front of his home city fans at Elland Road in Leeds, England.
The English boxer dominated and looked to have done enough to earn a unanimous decision after nullifying Selby's skills and sharp reflexes.
"I can't put it into words -- I've worked hard over the last 18 weeks, I got into the ring with the expectations of the whole city," Warrington said. "It was sheer grit and determination, and the crowd got me through it tonight.
"The crowd kept pushing me forward and giving me that second gear when I needed it. Lee is a very good fighter, and every fighter who has rushed in has come unstuck.
"It was a case of being educated and taking our chance when it came, and I out-boxed a boxer tonight."
But another all-British world title fight with Northern Ireland's Carl Frampton (25-1, 14 KOs) might have to wait for Warrington, according to promoter Frank Warren.
"Carl is fighting in Belfast on August 18, and we will work out where we go with that next week, and then we have that fight eventually," Warren said.
"I would love that fight, I would love him to come to Belfast to fight me," Frampton said.
Whomever Frampton fights next, it is unlikely to be Welshman Selby, who will have to claw himself back into contention at featherweight or step up a division.
Warrington's tenacity meant Selby could not establish any authority through his boxing skills and reflexes, which usually keep him out of trouble.
Selby (26-2, 9 KOs), 31, was left in a dogfight from the second round after being cut, as Warrington's tactics and stamina earned him a victory in his first world title fight.
Warrington (27-0, 6 KOs), 27, who walked to the ring to the sounds of "I Predict A Riot" performed live by hit band Kaiser Chiefs, has steadily improved, but there are others -- including Frampton -- ahead of him in the pecking order in the featherweight division, which is loaded with talent.
Not only was this Warrington's biggest night, but also Selby's, whose career to this point had lacked the big occasion despite this being his sixth title defense in a three-year reign.
Despite the backing of a crowd of over 20,000, it was Selby who started as the favorite. Warrington's form over the past year or so, which included impressive wins over Dennis Ceylan and Kiko Martinez in 2017, had reduced the odds, but getting the better of Selby's slick skills was always going to be a tall order for the home hero.
However, Selby could not establish a rhythm behind his jab early on, and Warrington had some success on the counter, including a left hook in the first round.
In the second round, Selby was in crisis after being cut above the left eye from a clash of heads. Warrington landed some hooks as Selby looked rattled and hurt toward the end of the second round.
Selby found some composure in the third round as he began firing out the jab and making Warrington miss.
Blood continued to stream down Selby's face, and the champion's reflexes, usually so sharp, were not enough to keep him out of range in the fourth and fifth rounds.
Warrington got through with right hands in the fifth round, and the fight was drifting away from Selby at the halfway point.
Warrington landed two more hard right hands in the sixth round before the referee asked the ringside doctor to inspect Selby's damaged left eye.
When the fight resumed, Selby looked in disarray as Warrington swarmed all over him and landed clean shots.
Warrington, who seemed to have more snap and energy, did not give Selby time to put his combinations together like his in recent defenses.
Warrington picked off Selby with his jab early in the 10th round as he continued to land the cleaner and harder punches.
Warrington landed a thudding right to send Selby bouncing off the ropes in the 10th round, and the challenger's jab was razor-sharp in the 11th.
Selby is not known for his knockout power, and by the last round, the fight was lost as Warrington landed more blows to seal what should have been a unanimous decision win.
On Saturday's undercard, Nicola Adams resumed her professional career with a first-round win over Soledad del Valle Frias.
Flyweight Adams (4-0, 3 KOs), a two-time Olympic gold medalist for Great Britain, in 2012 and 2016, stopped the Argentine for her fourth professional win from as many fights.
But the win was controversial, since Adams finished off her opponent in 2 minutes, 46 seconds of a bout that was supposed to be two-minute rounds.
Adams, 35, was just too good for Frias (13-12- 4, 4 KOs) in front of her home-city fans in Leeds and is aiming to fulfil her career aspirations within the next two years before retiring.
It ended a five-month ring absence for Adams, who it was revealed last month had split from fiancée Marlen Esparza, an American boxer who is now a potential opponent for the Englishwoman, after a two-year relationship.
Adams has also had to contend with her mother Dee's breast cancer diagnosis in the past year.