British light-heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a majority decision in a close ten-round fight at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful single shots in a contest where the styles never quite clicked, with excessive holding disrupting the contest.
The scoring judges judged it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They succeed," the victor said in the ringside as he was faced boos from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts believed Parker, 31, merited the victory but the British boxer experienced the second setback of his 28-bout career.
The Champion Earns Triumph in Dull Encounter
The fighter's advancement has stalled in the past few years through contract problems and considerable time of inactivity.
Previously predicted as the rising talent of British boxing, he now finds himself trying to achieve expectations - maybe in what appears to be a last chance - under fresh management.
He began cautiously, with neither fighter willing to be aggressive in a calculated initial rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after breaking his hand in the contest, was competing in only his second fight at light heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for the favorite, who operated with a protective stance to narrowly win the better periods.
The spectators' acceptance diminished amid constant clinching, with Parker slipping to the canvas various instances during clinches.
The underdog finished the stronger, but many rounds were hard to judge. Although, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of hard hitter David Benavidez, and Russian star Bivol leading the category, the road to world glory - judging by this showing - still looks steep.
Hatton Tribute Motivates Local Rivalry Contest
In the secondary fight, Arthur overcame Rea by close verdict in a excellent Manchester vs Manchester battle to win the continental title.
The stadium became quiet for a extremely emotional tribute before the fight as ten bells rang in honor of local hero Hatton, who passed away at age 46 in September.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the last bell faded, the quiet gave way to a chant of "there's only one Hatton".
The action during the bout reflected the feeling. The eventual winner was knocked down by a significant blow directly to the face in the initial stage, rising shakily to his footing on the referee's count.
But the Manchester United-red shorts of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was injured quickly, significant bruising appearing under his orbital area as the fighters landed hard punches.
Rea, 27, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the action rarely dropped over the full distance.
Arthur narrowly won the result with official scores of even score, 115-113 and clearer margin, but both fighters were persistent and full of heart, exactly what their inspiration Hatton embodied.
