British light-heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive ten-round fight at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a match where the approaches never quite clicked, with frequent clinching marring the contest.
The scoring judges had it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my finest showing but how do champions respond? They win," Buatsi commented in the arena as he was faced negative reactions from the audience.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Various analysts believed Parker, 31, merited the decision but the British boxer suffered the second defeat of his 28-fight career.
Buatsi Claims Win in Slow Affair
Buatsi's progress has stalled in recent times through management issues and long spells of inactivity.
Once tipped as the next star of UK boxing, he now stands trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors ready to overcommit in a tentative initial rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was participating in his second fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a protective stance to narrowly win the cleaner rounds.
The spectators' acceptance wore thin amid constant clinching, with Parker slipping to the canvas several times during clinches.
The underdog closed well, but many rounds were difficult to score. Although, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just one round.
Buatsi progresses, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - judging by this showing - still seems difficult.
Hatton Memorial Fuels Manchester Derby Battle
In the secondary fight, Arthur overcame Rea by divided decision in a terrific local rivalry battle to secure the continental championship.
The arena became quiet for a extremely emotional memorial before the fight as 10 bells rang in honor of local hero Ricky Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast match card in the location since Hatton's death. As the concluding sound faded, the quiet transitioned to a roar of "only one Ricky Hatton".
The competition within the ring reflected the sentiment. The eventual winner was sent to the canvas by a left hook flush on the jaw in the early round, getting up unsteadily to his footing on the referee's count.
But the traditional red equipment of the fighter soon advanced again. From the other corner, Rea - in opposing blue - was damaged early, significant bruising appearing under his face as the fighters traded hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with effective uppercuts as the action hardly diminished over the full distance.
Arthur barely secured the verdict with scoring tallies of draw, narrow lead and clearer margin, but both fighters were determined and full of heart, exactly what their hero the legend embodied.
