British light-heavyweight Joshua Buatsi secured a victory yet underwhelming start to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a majority decision in a tight ten-round bout at the Manchester venue.
But the challenger found success, connecting with powerful single shots in a contest where the approaches didn't complement each other, with constant grabbing spoiling the contest.
Two judges judged it 96-94 for to the winner, with the third a even score.
"It wasn't my best showing but what do champions do? They prevail," Buatsi stated in the arena as he was faced boos from the audience.
The British fighter got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to earn a 20th pro success.
Some ringside observers felt the challenger, 31, deserved the victory but the contender suffered the second loss of his 28-fight career.
The Champion Claims Win in Uneventful Encounter
The fighter's advancement has slowed in the past few years through management issues and extended periods of lack of fights.
Once tipped as the rising talent of UK boxing, he now is positioned trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter willing to overcommit in a calculated opening few rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand in the contest, was competing in only his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for Buatsi, who operated with a protective stance to narrowly win the more effective rounds.
The crowd's patience diminished during frequent holding, with Parker going down several times during close exchanges.
Parker finished the stronger, but multiple periods were difficult to score. Nevertheless, ex-champion the boxing analyst - commentating on Dazn - had it particularly wide for Parker, giving Buatsi just one round.
Buatsi advances, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Memorial Fuels Manchester Derby Fight
In the co-main event, Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester battle to capture the European light heavyweight belt.
The stadium fell silent for a extremely emotional memorial before the fight as 10 bells rang in remembrance of local hero 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 final chime faded, the stillness gave way to a roar of "only one Ricky Hatton".
The action during the bout reflected the feeling. The eventual winner was knocked down by a left hook directly to the face in the second round, getting up unsteadily to his position on the count of eight.
But the red-colored shorts of Arthur soon came forward again. From the other corner, the opponent - in rival City blue - was damaged soon, significant bruising appearing under his eye as the fighters landed hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the action hardly diminished over 12 rounds.
Arthur barely secured the decision with official scores of 114-114, 115-113 and wider gap, but both fighters were relentless and brave, everything their hero Hatton embodied.
