Tony Bellew beat Nathan Cleverly in a split decision after a gruelling 12-round fight on Saturday night, avenging his 2011 defeat.
The Liverpool fighter edged the cruiserweight bout in front of his home crowd after moving ahead with a strong ninth round following close early exchanges.
The three judges scored it 114-115 116-112 115-113 to Bellew.
The winner is likely to face reigning WBO cruiserweight champion Marco Huck.
The British pair, who both weighed in at 14st 3lbs on Friday, both looked exhausted in the latter stages.
"I was getting tagged but I was just walking through it," Bellew told BBC Radio 5 live. "I love the sport and the glory of it - I just can't quit.
"I feel like crying - I'm so happy to get home to my three kids. Winning means so much to me. I was gutted about the split decision, I think I won nine rounds.
"I got him in the corner and roughed him up, it was old school. It was only after seven rounds when I realised I wouldn't get hit with a big shot. I began to creep forward and he was always on the back foot."
|Former world super-middleweight champion Richie Woodhall on BBC Radio 5 live|
|"Tremendous performance from Bellew. I am still unsure about what has happened to Nathan Cleverly. I suspect he has an injury to his right hand."|
Bellew's victory gave him revenge for a majority decision defeat to the Welshman in their WBO light-heavyweight showdown at the same Echo Arena venue three years ago.
Since their first fight both men suffered knockout losses against Adonis Stevenson and Sergey Kovalev respectively.
After a cagey first few rounds dominated by jabs from both sides, Bellew stepped up the pace in the seventh, without ever landing a significant blow.
Cleverly spent most of the ninth round with his back against the ropes but Bellew missed too often and, as the fight became ragged, the Welshman clung on, only to lose on a split decision.
Cleverly said: "It shows my character, I have come up a weight. His strength showed in the second half. He was using his strength and made it pay. One-one, maybe we will have third fight."
In response, Bellew said he would "fight anywhere", including the Millennium Stadium in Cardiff. "Let's do it," he added.
The other fights on the undercard:
WBA super-bantamweight title: Scott Quigg beat Hidenori Otake on points
WBA bantamweight title fight: Jamie McDonnell stopped Javier Chacon in the 10th round
British heavyweight title eliminator: Anthony Joshua stopped Michael Sprott in first round
"I have to go back to the room and do another nine rounds of pads now. I have to finish off what I started. I don't like to make predictions but I will train to get in peak condition and I reckon I will be able to take Kevin Johnson out next. It will be a good move for me."
WBC Silver super-middleweight title: George Groves stopped Denis Douglin in the seventh round
Groves: "My coach says it was a 5/10 display. I'll have a look back at it, but I'd probably agree. Fighting a southpaw is a new experience and just what I needed. I had to change my distance and range and find my radar to someone with an opposite style.
"It's good to get a stoppage and now I want to roll on for the next one. I want the quickest route to a world title."
James DeGale stopped Marco Antonio Periban in the third round
DeGale: "He's never been stopped, Sakio Bika couldn't stop him and I was only getting warmed up. That left hand is my shot at the moment. I hit him and he was stumbling around, he wasn't in a position to carry on.
"I'll come out and watch George Groves but don't worry about him, I am the mandatory for the IBF title - I want to make history.
"I like Carl [Froch] but it feels like he doesn't want to fight me, I respect him but I think he's being a bit of a coward not fighting me - fight me or vacate the title."
Promoter Eddie Hearn added: "The Froch fight is a great fight, the Groves fight is a great fight, but James will fight for a World title in his next fight whomever there is."
Callum Smith beat Nikola Sjekloca on points after 12 rounds
Smith said: "My Nan passed away last week and she would've been 80 tonight. It was a tough week but going to the gym and getting away from it all maybe helped.
"He's been to points twice with Bika and Abraham but I hurt him with body shots and that shows I can hurt some good fighters. It's another box ticked with the 12 rounds under the belt."