UK light heavyweight Joshua Buatsi secured a victory yet underwhelming debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful clean blows in a fight where the approaches didn't complement each other, with constant grabbing marring the action.
Two judges scored it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my best display but how do champions respond? They prevail," the victor stated in the arena as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers thought Parker, thirty-one, should have been awarded the win but the British boxer experienced the second setback of his 28-fight professional journey.
Buatsi Claims Win in Dull Match
Buatsi's progress has stalled in recent times through contract problems and considerable time of inactivity.
Previously predicted as the future of British boxing, he now finds himself trying to achieve expectations - perhaps in what seems like a last chance - under recent support.
He started carefully, with the two boxers prepared to overcommit in a tentative opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second appearance at light-heavyweight.
By the halfway stage, Parker had made it competitive, making life awkward for the favorite, who utilized a solid defense to narrowly win the cleaner rounds.
The crowd's patience diminished during regular grabbing, with Parker going down multiple occasions during clinches.
The underdog closed well, but multiple periods were hard to judge. However, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Tribute Motivates Manchester Derby Battle
In the supporting bout, Arthur beat Rea by divided decision in a terrific Manchester vs Manchester battle to win the continental belt.
The venue fell silent for a deeply poignant memorial prior to the bout as ten bells sounded in honor of Manchester's own Hatton, who died 46 years old in September.
It was the first major televised match card in the urban center since the passing of Hatton. As the final chime disappeared, the stillness gave way to a shout of "there's only one Hatton".
The action within the ring reflected the feeling. The eventual winner was sent to the canvas by a significant blow squarely on the face in the second round, standing uncertainly to his feet on the eight count.
But the Manchester United-red attire of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was damaged early, noticeable damage forming under his eye as the fighters exchanged powerful shots.
Rea, 27, delivered effective strikes but Arthur, 34, responded in kind with effective uppercuts as the intensity hardly diminished over 12 rounds.
Arthur edged the decision with official scores of 114-114, close margin and 115-112, but the two athletes were relentless and full of heart, everything their inspiration the legend stood for.
