British light-heavyweight Joshua Buatsi made a winning yet underwhelming start to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a competitive 10-round contest at the boxing arena.
But Parker found success, connecting with powerful clean blows in a fight where the styles never quite clicked, with excessive holding marring the action.
The officials had it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my greatest display but what defines champions? They win," the victor said in the ringside as he was met by boos from the crowd.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a 20th pro success.
Various analysts thought Parker, thirty-one, merited the decision but the contender experienced the second loss of his 28-match career.
Buatsi Earns Victory in Slow Encounter
His career development has slowed in recent times through management issues and considerable time of inactivity.
Earlier forecast as the next star of the British fight scene, he now stands trying to realize his potential - maybe in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors prepared to be aggressive in a tentative early stages.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after breaking his hand mid-fight, was participating in his second fight at light-heavyweight.
By the middle rounds, Parker had made it competitive, causing problems for Buatsi, who utilized a protective stance to barely take the more effective periods.
The crowd's patience diminished during constant clinching, with Parker falling to the floor multiple occasions during clinches.
The underdog ended stronger, but multiple periods were hard to judge. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Hatton Homage Fuels Manchester Derby Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by split-decision in a outstanding all-Manchester contest to secure the European light heavyweight championship.
The arena grew hushed for a extremely emotional tribute before the fight as 10 bells rang in honor of local hero Hatton, who passed away 46 years old in last month.
It was the premier televised fight night in the urban center since the passing of Hatton. As the final chime ended, the stillness transitioned to a chant of "there's only one Hatton".
The competition inside the ropes matched the feeling. Arthur was floored by a significant blow directly to the jaw in the early round, getting up unsteadily to his position on the referee's count.
But the red-colored equipment of the fighter soon came forward again. On the opposite side, the opponent - in rival City blue - was injured quickly, heavy swelling forming under his eye as the pair landed hard punches.
The challenger, 27, connected with strong blows but the champion, thirty-four, responded in kind with effective uppercuts as the action seldom decreased over 12 rounds.
Arthur barely secured the verdict with official scores of 114-114, close margin and wider gap, but each competitor were persistent and full of heart, exactly what their idol Hatton represented.
