British light-heavyweight Joshua Buatsi secured a victory yet unimpressive start to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a judges' verdict in a close 10-round fight at the Manchester venue.
But the challenger landed significant shots, delivering effective individual punches in a match where the approaches failed to mesh, with excessive holding marring the fight.
The officials scored it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my greatest performance but how do champions respond? They succeed," the victor commented in the ringside as he was greeted with negative reactions from the crowd.
The British fighter returned to winning ways after his initial pro loss - an epic battle with his previous opponent in February - to claim a 20th career victory.
Various analysts believed the challenger, 31, should have been awarded the win but the British boxer endured the second defeat of his 28-fight professional journey.
Buatsi Secures Victory in Slow Encounter
Buatsi's progress has plateaued in recent years through promotional disputes and considerable time of lack of fights.
Once tipped as the future of the British fight scene, he now finds himself trying to achieve expectations - possibly in what seems like a final roll of the dice - under recent support.
He began cautiously, with both competitors prepared to take risks in a cagey early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in 2022 after damaging his hand mid-fight, was participating in his second fight at light-heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for Buatsi, who operated with a solid defense to barely take the cleaner rounds.
The audience's tolerance decreased because of frequent holding, with the challenger falling to the floor various instances during clinches.
The underdog ended stronger, but several stanzas were difficult to score. Nevertheless, previous titleholder Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just one round.
The victor advances, but with the likes of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates Local Rivalry Contest
In the co-main event, Lyndon Arthur defeated Bradley Rea by split-decision in a outstanding Manchester vs Manchester contest to win the continental belt.
The arena fell silent for a deeply poignant tribute prior to the bout as ten bells rang in remembrance of local hero Hatton, who passed away 46 years old in September.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the last bell faded, the silence became a roar of "there's just one Ricky Hatton".
The action inside the ropes reflected the sentiment. Arthur was floored by a left hook squarely on the jaw in the second round, rising shakily to his footing on the count of eight.
But the red-colored attire of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was damaged soon, heavy swelling developing under his eye as the pair traded punishing blows.
Rea, 27, delivered effective strikes but Arthur, thirty-four, matched the intensity with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor narrowly won the decision with judges scorecards of 114-114, close margin and wider gap, but each competitor were persistent and courageous, everything their inspiration the legend stood for.
