British light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a tight 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful individual punches in a contest where the techniques never quite clicked, with constant grabbing spoiling the contest.
The officials scored it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my best showing but how do champions respond? They prevail," Buatsi stated in the ringside as he was met by boos from the audience.
The British fighter bounced back after his maiden career setback - an epic battle with Callum Smith in February - to claim a twentieth professional win.
Some ringside observers thought Parker, 31, deserved the victory but the contender suffered the second setback of his 28-bout career.
Buatsi Secures Win in Dull Affair
The fighter's advancement has slowed in recent times through contract problems and considerable time of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a last chance - under fresh management.
He started carefully, with neither fighter willing to take risks in a cagey initial rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in 2022 after damaging his hand during the bout, was competing in only his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a solid defense to barely take the cleaner periods.
The audience's tolerance diminished because of constant clinching, with the challenger going down multiple occasions during grappling.
The underdog ended stronger, but several stanzas were hard to judge. Although, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor moves on, but with the caliber of hard hitter Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Homage Motivates All-Manchester Battle
In the secondary fight, Arthur overcame Bradley Rea by divided decision in a outstanding Manchester vs Manchester fight to capture the European light-heavyweight belt.
The venue fell silent for a profoundly moving tribute ahead of the contest as 10 bells rang in honor of local hero Hatton, who died 46 years old in September.
It was the premier televised fight night in the urban center since Hatton's passing. As the final chime disappeared, the silence transitioned to a chant of "there's only one Hatton".
The action inside the ropes reflected the feeling. The eventual winner was floored by a powerful punch directly to the jaw in the second round, standing uncertainly to his feet on the referee's count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. From the other corner, Rea - in rival City blue - was injured early, heavy swelling forming under his orbital area as the duo exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action rarely dropped over twelve rounds.
Arthur barely secured the decision with official scores of 114-114, close margin and wider gap, but the two athletes were persistent and brave, everything their inspiration Hatton stood for.
