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Anthony Crolla lost his WBA lightweight title to Jorge Linares after a gruelling battle at Manchester Arena.
Crolla, 29, was making the second defence of the title he won from Colombia's Darleys Perez last November.
After a slow start Crolla appeared to have found his range by the middle rounds, although the challenger landed with the more eye-catching punches.
But the Venezuelan's superior skills trumped Crolla's constant pressure and he was awarded a unanimous decision.
Two judges thought the fight was close, awarding it 115-114 and 115-113 to Linares, while the third judge had the challenger winning 117-111.
Linares immediately offered Crolla a rematch, while the Manchester boxer's promoter left the crowd in little doubt that the two men would do it again.
"I am deeply disappointed. I have no complaints, but I am sorry I couldn't do it for this crowd," Crolla told Radio 5 live.
"He's the best man I've ever been in a ring with, he's very fast and sharp and it was a pleasure to be in there with him.
"I gave it everything, it wasn't through a lack of trying, the difference was I took one or two hard counter-shots, which I was warned about by my team, and I paid the price.
"I am gutted, it's heart-breaking to lose the belt, but I will come back from this."
Crolla was bidding to emulate fellow Mancunian Ricky Hatton, who beat Kostya Tszyu at the same venue in 2005 to secure the coveted Ring magazine light-welterweight title and lay claim to being the best in the division.
In his only previous bout on British soil last May, Linares climbed off the canvas before stopping Kevin Mitchell in 10 rounds at London's O2 arena.
Former three-weight world champion Linares, 31, made one more defence of his WBC lightweight belt before he was forced to vacate because of inactivity.
There was little to separate the boxers in the opening two rounds, although the challenger, who has not lost for more than four years, did land with a couple of spiteful looking lefts to the body.
Linares stunned the champion with a dazzling combination at the start of the third and was unmoved when Crolla got through with an uppercut on the bell.
Crolla appeared to have found his range at the start of the fourth, during which Linares was warned twice for low blows. The second, a savage left hook, momentarily took the wind out of the champion's sails.
Linares was cut over the left eye at the start of the fifth and it appeared the momentum was beginning to turn towards the champion, who was backing Linares up and landing with left jabs and hooks.
The fight opened up in the sixth, Linares strafing Crolla with fast hands before the champion hit back with a juddering uppercut. When Linares landed with a couple of clubbing overhand rights, Crolla appeared to be in serious trouble.
But he soaked up the punishment on the ropes before coming out punching again.
By the seventh the fight had become a grim war of attrition and the eighth followed in the same fashion, although Linares threw the more hurtful shots.
Crolla probably nicked the ninth but it was difficult to separate the two men as they entered the championship rounds, Crolla having been the busier but Linares having arguably landed with the more eye-catching punches.
Linares had the better of the 10th while the penultimate round was a case of sucking it up before the final push, with Linares barely throwing a right hand.
Linares came out all guns blazing in the 12th, jerking Crolla's head back with overhand rights and flashing left hooks. Crolla landed with a juddering left hook as the fight enter its final stages but Linares remained entirely unruffled.
The Tokyo-based Linares, whose blazing hand speed and variety of punches meant Crolla could have no complaint about the outcome, also claimed the coveted Ring magazine lightweight title.
"I want to tell all the people thank you very much," said Linares. "We gave Manchester a beautiful fight and we can do it again.
"I hurt my hand in the sixth, and backed off a bit, in the 10th I told my corner I would close out the victory and I did and that's what got me the victory."
Crolla has experienced a stratospheric rise through the ranks since suffering a fractured skull and broken ankle when confronting burglars in 2014.
And his defeat by Linares, his fifth in 39 professional fights, does not spell the end of his elite-level career by any means, with other options out there apart from an immediate rematch
A match against former school-mate and WBO champion Terry Flanagan could also now happen, if promotional obstacles can be surmounted.
In June, Flanagan claimed his promoter Frank Warren had offered Crolla the fight but that Hearn turned it down. Hearn said that Flanagan did not bring enough money to the table and opted for a match with Ismael Barroso instead.
BBC Sport boxing expert Steve Bunce: "That was a fantastic performance from a great fighter. We've seen tenacity, skill and composure from Linares.
"Crolla played his part from the opening round but his power seeped away from him towards the end. Not his heart, just his power. I think Crolla was close to exhaustion."
Former world champion Richie Woodhall on Radio 5 live: "Linares is a true champion and didn't let the crowd get to him.
"Crolla had to take some hard shots, he showed dogged determination and boxed intelligently but he took one too many shots. Linares has very quick hands and that helped him control the fight at the end."
On the undercard
Jack Arnfield of Blackpool secured the fringe WBA 'international' middleweight title with a unanimous decision over London's John Ryder.
Boston's Callum Johnson claimed the vacant Commonwealth light-heavyweight title with a ninth-round knockout of tough Namibian Wilberforce Shihepo.
Hosea Burton, like Johnson trained by Joe Gallagher, was meant to have defended his British light-heavyweight title against Frank Buglioni only for Buglioni to withdraw because of a cut.
Watched by his cousin Tyson Fury, who withdrew from his scheduled rematch with Wladimir Klitschko on Friday, Burton stopped Mexican replacement Fernando Castaneda in three rounds to stay unbeaten in 18 pro fights.
Conor Benn, boxing over six rounds for the first time, made it five wins from five professional fights by outpointing Middlesbrough's Ross Jameson.
Benn, son of British boxing great Nigel, looked raw, was easily hit and ran out of steam in the final round but is only 19 and has plenty of time to improve.