British light heavyweight Joshua Buatsi made a winning yet disappointing debut to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a tight 10-round bout at the boxing arena.
But Parker had his moments, connecting with powerful single shots in a contest where the styles failed to mesh, with excessive holding disrupting the contest.
The scoring judges judged it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my finest showing but what defines champions? They win," Buatsi commented in the arena as he was faced negative reactions from the crowd.
The Londoner got back to winning after his first professional defeat - an epic battle with Callum Smith in February - to secure a 20th pro success.
Various analysts thought Parker, 31, should have been awarded the decision but the Derbyshire fighter experienced the second defeat of his 28-fight professional journey.
Buatsi Earns Triumph in Slow Encounter
The fighter's advancement has stalled in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what appears to be a last chance - under fresh management.
He began cautiously, with neither fighter prepared to be aggressive in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was making just his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for the favorite, who utilized a solid defense to narrowly win the more effective stanzas.
The audience's tolerance wore thin during frequent holding, with Parker going down multiple occasions during clinches.
The underdog ended stronger, but many rounds were difficult to score. Nevertheless, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just one round.
Buatsi progresses, but with the caliber of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Ricky Hatton Memorial Inspires Local Rivalry Fight
In the secondary fight, Arthur overcame Rea by split-decision in a terrific all-Manchester fight to win the European light-heavyweight championship.
The venue grew hushed for a extremely emotional memorial before the fight as a bell ceremony tolled in memory of local hero Ricky Hatton, who succumbed 46 years old in September.
It was the premier televised match card in the urban center since Hatton's death. As the concluding sound disappeared, the silence gave way to a shout of "there's just one Hatton".
The action inside the ropes matched the feeling. The eventual winner was sent to the canvas by a left hook flush on the jaw in the initial stage, standing uncertainly to his footing on the count of eight.
But the Manchester United-red attire of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was injured soon, noticeable damage developing under his face as the pair traded powerful shots.
Rea, 27, connected with strong blows but Arthur, thirty-four, responded in kind with effective uppercuts as the pace hardly diminished over the full distance.
The victor barely secured the result with official scores of 114-114, narrow lead and 115-112, but each competitor were determined and full of heart, all the qualities their idol Hatton represented.
