British light heavyweight Joshua Buatsi secured a victory yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a split decision in a close 10-round fight at the Manchester venue.
But Parker found success, connecting with powerful single shots in a fight where the approaches failed to mesh, with constant grabbing marring the action.
The officials judged it 96-94 for to the winner, with the final judge a 95-95.
"It wasn't my finest performance but what defines champions? They prevail," the victor stated in the arena as he was met by boos from the audience.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Some ringside observers believed Parker, thirty-one, deserved the decision but the British boxer suffered the second loss of his 28-fight professional journey.
Buatsi Secures Victory in Uneventful Encounter
Buatsi's progress has plateaued in the past few years through promotional disputes and considerable time of lack of fights.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - possibly in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter willing to take risks in a cagey early stages.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after breaking his hand during the bout, was competing in only his second bout at the higher weight class.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who operated with a tight guard to narrowly win the cleaner stanzas.
The audience's tolerance wore thin because of regular grabbing, with Parker slipping to the canvas multiple occasions during clinches.
The underdog closed well, but several stanzas were difficult to score. Although, former world champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just a single round.
Buatsi progresses, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Motivates Manchester Derby Battle
In the secondary fight, Arthur overcame Rea by split-decision in a outstanding Manchester vs Manchester battle to capture the European light-heavyweight championship.
The stadium grew hushed for a deeply poignant tribute ahead of the contest as ten bells sounded in remembrance of the city's native Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the last bell disappeared, the stillness became a chant of "there's only one Hatton".
The fighting within the ring reflected the feeling. Arthur was knocked down by a powerful punch squarely on the jaw in the second round, rising shakily to his position on the eight count.
But the traditional red shorts of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was marked up early, heavy swelling developing under his orbital area as the duo exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with powerful upward punches as the intensity rarely dropped over twelve rounds.
Arthur narrowly won the decision with official scores of draw, close margin and clearer margin, but both fighters were determined and brave, everything their inspiration the legend represented.
