UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming start to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a tight ten-round contest at the Manchester venue.
But the challenger landed significant shots, connecting with powerful clean blows in a fight where the styles never quite clicked, with excessive holding disrupting the contest.
Two judges had it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what do champions do? They succeed," the victor stated in the ringside as he was met by boos from the spectators.
The Londoner got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts believed Parker, 31, deserved the decision but the British boxer experienced the second setback of his 28-match career.
The Champion Claims Triumph in Dull Affair
His career development has stalled in recent years through management issues and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to realize his potential - perhaps in what seems like a last chance - under recent support.
He began cautiously, with neither fighter willing to be aggressive in a tentative opening few rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after damaging his hand mid-fight, was making just his second bout at the higher weight class.
By the middle rounds, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to barely take the better rounds.
The spectators' acceptance wore thin amid regular grabbing, with the challenger going down various instances during clinches.
The underdog ended stronger, but multiple periods were difficult to score. However, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Hatton Homage Inspires Manchester Derby Contest
In the co-main event, Lyndon Arthur defeated Rea by split-decision in a excellent local rivalry fight to capture the European light heavyweight championship.
The stadium grew hushed for a profoundly moving homage prior to the bout as 10 bells rang in remembrance of the city's native Ricky Hatton, who died 46 years old in September.
It was the premier televised fight night in the city since Hatton's passing. As the final chime faded, the quiet transitioned to a roar of "there's only one Hatton".
The competition during the bout equaled the emotion. Arthur was floored by a significant blow squarely on the chin in the initial stage, getting up unsteadily to his footing on the referee's count.
But the red-colored attire of the fighter soon advanced again. From the other corner, the opponent - in competitive blue - was marked up quickly, heavy swelling developing under his face as the duo traded powerful shots.
Rea, 27, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the action seldom decreased over twelve rounds.
Arthur barely secured the decision with official scores of even score, close margin and clearer margin, but both fighters were relentless and full of heart, all the qualities their idol the legend represented.
