UK light heavyweight Joshua Buatsi made a winning yet disappointing start to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a close ten-round fight at the Co-op Live Arena.
But the challenger had his moments, landing some telling single shots in a fight where the styles failed to mesh, with constant grabbing marring the fight.
The scoring judges had it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my finest display but what do champions do? They succeed," Buatsi stated in the ringside as he was greeted with disapproval from the audience.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Several boxing experts felt Parker, thirty-one, merited the decision but the contender experienced the second defeat of his 28-match professional journey.
Buatsi Earns Triumph in Dull Encounter
His career development has plateaued in the past few years through management issues and considerable time of lack of fights.
Once tipped as the next star of British boxing, he now stands trying to achieve expectations - maybe in what seems like a final roll of the dice - under recent support.
He opened tentatively, with neither fighter willing to overcommit in a tentative early stages.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand during the bout, was making just his second appearance at the higher weight class.
By the halfway stage, the underdog had stayed in contention, causing problems for the favorite, who utilized a tight guard to barely take the cleaner stanzas.
The crowd's patience diminished amid frequent holding, with Parker falling to the floor various instances during grappling.
The underdog closed well, but many rounds were challenging to assess. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, giving Buatsi just one round.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Tribute Motivates Manchester Derby Battle
In the supporting bout, Lyndon Arthur overcame Rea by close verdict in a terrific local rivalry contest to capture the European light-heavyweight title.
The arena became quiet for a deeply poignant tribute before the fight as 10 bells tolled in memory of the city's native Ricky Hatton, who passed away at age 46 in last month.
It was the premier televised boxing event in the location since the passing of Hatton. As the last bell ended, the silence became a shout of "only one Ricky Hatton".
The competition during the bout reflected the sentiment. Arthur was knocked down by a powerful punch directly to the face in the second round, standing uncertainly to his position on the eight count.
But the Manchester United-red attire of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was injured soon, significant bruising appearing under his orbital area as the fighters exchanged hard punches.
The challenger, 27, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the action seldom decreased over the full distance.
The victor barely secured the verdict with official scores of even score, narrow lead and clearer margin, but each competitor were persistent and full of heart, exactly what their hero the legend embodied.
