UK light-heavyweight Joshua Buatsi secured a victory yet disappointing debut to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger had his moments, delivering effective single shots in a contest where the approaches didn't complement each other, with constant grabbing disrupting the fight.
The scoring judges judged it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my best display but what defines champions? They win," the victor stated in the arena as he was faced negative reactions from the crowd.
The Londoner got back to winning after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a 20th career victory.
Various analysts believed Parker, thirty-one, deserved the win but the contender suffered the second defeat of his 28-fight career.
The Champion Secures Win in Dull Match
His career development has plateaued in the past few years through management issues and extended periods of lack of fights.
Once tipped as the rising talent of the British fight scene, he now finds himself trying to achieve expectations - maybe in what seems like a final roll of the dice - under fresh management.
He began cautiously, with both competitors prepared to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after damaging his hand in the contest, was making just his second fight at the higher weight class.
By the middle rounds, Parker had made it competitive, making life awkward for the favorite, who worked behind a solid defense to narrowly win the more effective periods.
The spectators' acceptance wore thin because of constant clinching, with the challenger falling to the floor multiple occasions during clinches.
The underdog closed well, but multiple periods were challenging to assess. Nevertheless, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - judging by this showing - still appears challenging.
Hatton Tribute Motivates Local Rivalry Battle
In the supporting bout, Arthur overcame Rea by close verdict in a excellent local rivalry battle to win the European light-heavyweight championship.
The venue fell silent for a profoundly moving tribute prior to the bout as 10 bells rang in remembrance of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised fight night in the location since Hatton's passing. As the final chime faded, the stillness became a roar of "only one Hatton".
The action within the ring equaled the feeling. The eventual winner was knocked down by a powerful punch flush on the chin in the initial stage, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red equipment of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was marked up quickly, heavy swelling appearing under his face as the duo landed punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the pace hardly diminished over twelve rounds.
The victor narrowly won the result with official scores of draw, close margin and clearer margin, but both fighters were persistent and brave, everything their hero the legend embodied.
