UK light-heavyweight Joshua Buatsi earned a win yet unimpressive start to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a close ten-round bout at the boxing arena.
But Parker found success, connecting with powerful individual punches in a match where the styles failed to mesh, with excessive holding disrupting the contest.
The scoring judges had it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my finest performance but what defines champions? They succeed," Buatsi commented in the arena as he was faced boos from the crowd.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, should have been awarded the decision but the British boxer endured the second defeat of his 28-bout professional journey.
Buatsi Secures Victory in Slow Affair
His career development has stalled in the past few years through management issues and considerable time of inactivity.
Earlier forecast as the future of the British fight scene, he now finds himself trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with the two boxers willing to overcommit in a tentative 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 bout at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a protective stance to edge the more effective rounds.
The spectators' acceptance diminished amid regular grabbing, with the challenger falling to the floor various instances during grappling.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, former world champion Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the presence of power puncher David Benavidez, and Russian champion Bivol ruling the division, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Tribute Fuels Manchester Derby Contest
In the co-main event, Arthur overcame Rea by divided decision in a outstanding Manchester vs Manchester battle to secure the European light heavyweight championship.
The venue grew hushed for a profoundly moving tribute ahead of the contest as a bell ceremony sounded in memory of local hero Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast match card in the location since Hatton's passing. As the concluding sound faded, the stillness transitioned to a chant of "there's only one Hatton".
The fighting inside the ropes equaled the emotion. The eventual winner was floored by a left hook directly to the jaw in the early round, getting up unsteadily to his footing on the eight count.
But the traditional red equipment of Arthur soon came forward again. From the other corner, the opponent - in opposing blue - was marked up early, noticeable damage forming under his eye as the fighters traded punishing blows.
The challenger, 27, connected with strong blows but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity seldom decreased over the full distance.
Arthur barely secured the decision with judges scorecards of draw, 115-113 and wider gap, but each competitor were determined and brave, all the qualities their idol Hatton stood for.
