British light heavyweight Joshua Buatsi earned a win yet unimpressive debut to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a close ten-round fight at the Co-op Live Arena.
But the challenger found success, connecting with powerful single shots in a fight where the techniques never quite clicked, with excessive holding marring the action.
The officials judged it 96-94 to the winner, with the third a 95-95.
"It wasn't my finest showing but what do champions do? They succeed," the victor said in the arena as he was faced disapproval from the crowd.
The Londoner got back to winning after his maiden career setback - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Some ringside observers thought Parker, 31, should have been awarded the victory but the Derbyshire fighter endured the second defeat of his 28-fight professional journey.
The Champion Secures Triumph in Dull Encounter
The fighter's advancement has stalled in recent times through management issues and considerable time of inactivity.
Earlier forecast as the next star of UK boxing, he now is positioned trying to fulfil that early promise - maybe in what appears to be a last chance - under fresh management.
He opened tentatively, with neither fighter willing to overcommit in a tentative early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was making just his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for Buatsi, who utilized a protective stance to barely take the cleaner periods.
The audience's tolerance wore thin amid regular grabbing, with the challenger slipping to the canvas various instances during clinches.
Parker ended stronger, but several stanzas were hard to judge. Nevertheless, ex-champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Homage Inspires Local Rivalry Fight
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a excellent all-Manchester battle to win the continental championship.
The venue fell silent for a deeply poignant tribute prior to the bout as ten bells rang in remembrance of local hero Ricky Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast match card in the urban center since the passing of Hatton. As the concluding sound faded, the stillness gave way to a roar of "there's just one Ricky Hatton".
The competition during the bout reflected the sentiment. The eventual winner was floored by a powerful punch directly to the face in the second round, standing uncertainly to his position on the referee's count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was damaged early, heavy swelling developing under his face as the duo exchanged punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the pace seldom decreased over the full distance.
The victor edged the result with scoring tallies of 114-114, 115-113 and 115-112, but the two athletes were relentless and brave, exactly what their hero the legend embodied.
