UK light-heavyweight Joshua Buatsi earned a win yet unimpressive debut to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a split decision in a competitive ten-round bout at the boxing arena.
But Parker had his moments, landing some telling clean blows in a fight where the styles didn't complement each other, with frequent clinching spoiling the action.
The officials scored it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest performance but what do champions do? They win," the victor stated in the arena as he was faced disapproval from the crowd.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Various analysts thought Parker, thirty-one, merited the win but the contender suffered the second setback of his 28-match professional journey.
The Champion Earns Win in Slow Encounter
Buatsi's progress has plateaued in recent times through management issues and considerable time of inactivity.
Previously predicted as the rising talent of British boxing, he now stands trying to achieve expectations - possibly in what feels like a last chance - under recent support.
He opened tentatively, with neither fighter ready to take risks in a cagey early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a solid defense to narrowly win the more effective stanzas.
The crowd's patience decreased during regular grabbing, with Parker falling to the floor multiple occasions during close exchanges.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Hatton Tribute Inspires All-Manchester Contest
In the supporting bout, Arthur beat Rea by split-decision in a terrific local rivalry fight to win the European light-heavyweight title.
The venue fell silent for a profoundly moving homage prior to the bout as a bell ceremony tolled in honor of Manchester's own Ricky Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the concluding sound ended, the silence transitioned to a shout of "there's only one Ricky Hatton".
The competition inside the ropes matched the feeling. The eventual winner was floored by a significant blow directly to the face in the early round, standing uncertainly to his footing on the count of eight.
But the Manchester United-red attire of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was marked up quickly, noticeable damage forming under his orbital area as the duo exchanged punishing blows.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with effective uppercuts as the action seldom decreased over 12 rounds.
The victor edged the verdict with judges scorecards of draw, 115-113 and 115-112, but each competitor were persistent and courageous, everything their inspiration the legend stood for.
