British light-heavyweight Joshua Buatsi earned a win yet underwhelming beginning to life under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a tight 10-round fight at the boxing arena.
But the challenger landed significant shots, connecting with powerful individual punches in a fight where the approaches didn't complement each other, with excessive holding spoiling the fight.
The officials judged it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my greatest display but how do champions respond? They succeed," Buatsi commented in the arena as he was met by boos from the spectators.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to claim a twentieth professional win.
Various analysts thought the challenger, 31, merited the victory but the Derbyshire fighter endured the second defeat of his 28-match career.
The Champion Secures Win in Dull Encounter
Buatsi's progress has stalled in recent times through management issues and considerable time of inactivity.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - maybe in what feels like a last chance - under recent support.
He opened tentatively, with the two boxers ready to take risks in a cagey opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after breaking his hand mid-fight, was making just his second bout at light heavyweight.
By the halfway stage, Parker had kept it close, causing problems for Buatsi, who utilized a tight guard to narrowly win the more effective periods.
The spectators' acceptance wore thin amid constant clinching, with the challenger slipping to the canvas various instances during clinches.
The underdog finished the stronger, but multiple periods were hard to judge. Although, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor advances, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the co-main event, Arthur beat Rea by split-decision in a excellent all-Manchester fight to secure the continental championship.
The venue grew hushed for a deeply poignant homage ahead of the contest as a bell ceremony rang in honor of local hero Ricky Hatton, who died 46 years old in last month.
It was the premier televised match card in the city since Hatton's passing. As the final chime faded, the silence transitioned to a roar of "there's just one Hatton".
The fighting within the ring matched the emotion. Arthur was knocked down by a left hook flush on the face in the second round, standing uncertainly to his position on the count of eight.
But the Manchester United-red attire of the fighter soon pressed ahead again. Across the ring, the opponent - in competitive blue - was injured soon, significant bruising appearing under his face as the duo traded hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with powerful upward punches as the pace seldom decreased over the full distance.
Arthur narrowly won the decision with scoring tallies of even score, close margin and wider gap, but both fighters were determined and brave, everything their inspiration Hatton embodied.
