UK light heavyweight Joshua Buatsi secured a victory yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a majority decision in a competitive ten-round fight at the Co-op Live Arena.
But Parker landed significant shots, landing some telling single shots in a contest where the techniques didn't complement each other, with frequent clinching marring the action.
Two judges had it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my finest display but how do champions respond? They win," the victor commented in the arena as he was met by disapproval from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in February - to claim a 20th career victory.
Some ringside observers felt the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter suffered the second defeat of his 28-fight professional journey.
Buatsi Secures Victory in Dull Match
Buatsi's progress has slowed in recent times through management issues and long spells of inactivity.
Earlier forecast as the next star of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with the two boxers ready to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was participating in his second appearance at light heavyweight.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who utilized a tight guard to edge the better periods.
The spectators' acceptance diminished because of regular grabbing, with the challenger going down multiple occasions during grappling.
Parker ended stronger, but many rounds were challenging to assess. However, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - based on this performance - still seems difficult.
Hatton Homage Motivates All-Manchester Battle
In the secondary fight, Lyndon Arthur beat Rea by divided decision in a excellent local rivalry battle to secure the European light-heavyweight title.
The arena became quiet for a extremely emotional memorial prior to the bout as a bell ceremony sounded in honor of the city's native Hatton, who succumbed 46 years old in September.
It was the first major televised match card in the urban center since Hatton's death. As the concluding sound ended, the silence gave way to a roar of "there's just one Hatton".
The competition inside the ropes reflected the emotion. The eventual winner was knocked down by a significant blow flush on the face in the initial stage, standing uncertainly to his position on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. On the opposite side, Rea - in rival City blue - was damaged soon, heavy swelling forming under his eye as the pair exchanged powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the action seldom decreased over 12 rounds.
Arthur narrowly won the decision with judges scorecards of even score, close margin and wider gap, but both fighters were persistent and full of heart, all the qualities their inspiration the legend represented.
