UK light heavyweight Joshua Buatsi earned a win yet unimpressive debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a split decision in a tight ten-round fight at the boxing arena.
But Parker had his moments, connecting with powerful individual punches in a fight where the styles never quite clicked, with excessive holding marring the fight.
Two judges had it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest display but how do champions respond? They prevail," the victor stated in the ringside as he was greeted with boos from the crowd.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts believed Parker, thirty-one, should have been awarded the victory but the contender experienced the second setback of his 28-bout professional journey.
Buatsi Earns Victory in Dull Match
Buatsi's progress has stalled in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the next star of British boxing, he now is positioned trying to fulfil that early promise - possibly in what feels like a last chance - under new promotional backing.
He started carefully, with both competitors willing to be aggressive in a calculated initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent 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 stayed in contention, creating difficulties for the favorite, who utilized a protective stance to edge the cleaner stanzas.
The audience's tolerance diminished during regular grabbing, with Parker falling to the floor several times during clinches.
The underdog ended stronger, but multiple periods were challenging to assess. Although, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Hatton Memorial Motivates All-Manchester Fight
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a excellent Manchester vs Manchester fight to capture the continental title.
The stadium grew hushed for a profoundly moving tribute ahead of the contest as a bell ceremony rang in remembrance of the city's native Hatton, who passed away 46 years old in recently.
It was the first major televised fight night in the city since Hatton's death. As the final chime faded, the silence transitioned to a roar of "there's just one Hatton".
The competition during the bout matched the emotion. Arthur was floored by a powerful punch flush on the chin in the early round, getting up unsteadily to his feet on the referee's count.
But the traditional red equipment of Arthur soon came forward again. From the other corner, the opponent - in opposing blue - was injured soon, heavy swelling appearing under his orbital area as the fighters exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the pace hardly diminished over twelve rounds.
The victor narrowly won the decision with scoring tallies of 114-114, close margin and clearer margin, but each competitor were persistent and full of heart, all the qualities their idol the legend stood for.
