UK light-heavyweight Joshua Buatsi made a winning yet unimpressive debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a split decision in a tight 10-round fight at the Co-op Live Arena.
But Parker landed significant shots, landing some telling clean blows in a fight where the techniques failed to mesh, with constant grabbing disrupting the action.
Two judges scored it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They win," the victor stated in the ringside as he was met by boos from the audience.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to secure a 20th pro success.
Some ringside observers felt the challenger, 31, merited the victory but the British boxer endured the second loss of his 28-fight career.
Buatsi Secures Win in Dull Encounter
Buatsi's progress has plateaued in the past few years through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to achieve expectations - possibly in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers prepared to take risks in a calculated initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was making just his second appearance at light-heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for Buatsi, who utilized a solid defense to narrowly win the more effective periods.
The audience's tolerance decreased during constant clinching, with the challenger slipping to the canvas several times during close exchanges.
Parker finished the stronger, but many rounds were difficult to score. However, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Homage Motivates Manchester Derby Battle
In the secondary fight, Arthur defeated Rea by split-decision in a terrific Manchester vs Manchester battle to win the continental title.
The arena became quiet for a profoundly moving memorial ahead of the contest as ten bells sounded in memory of Manchester's own Ricky Hatton, who passed away 46 years old in last month.
It was the first major televised match card in the urban center since Hatton's passing. As the last bell faded, the silence transitioned to a chant of "there's only one Hatton".
The action inside the ropes reflected the emotion. Arthur was knocked down by a powerful punch squarely on the face in the second round, getting up unsteadily to his footing on the count of eight.
But the red-colored equipment of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was injured early, noticeable damage forming under his eye as the pair landed punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the action hardly diminished over the full distance.
The victor edged the verdict with official scores of even score, narrow lead and wider gap, but both fighters were persistent and brave, all the qualities their hero Hatton represented.
