UK light heavyweight Joshua Buatsi earned a win yet disappointing start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a close 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective single shots in a contest where the techniques never quite clicked, with excessive holding spoiling the fight.
Two judges judged it 96-94 for to the winner, with the final judge a even score.
"It wasn't my greatest showing but how do champions respond? They prevail," the victor said in the arena as he was greeted with negative reactions from the spectators.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Some ringside observers thought Parker, 31, merited the decision but the Derbyshire fighter experienced the second defeat of his 28-match professional journey.
Buatsi Earns Victory in Uneventful Affair
His career development has plateaued in recent times through contract problems and considerable time of lack of fights.
Once tipped as the future of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers prepared to take risks in a cagey early stages.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who utilized a protective stance to barely take the better rounds.
The crowd's patience diminished amid frequent holding, with the challenger slipping to the canvas several times during clinches.
The underdog finished the stronger, but multiple periods were difficult to score. Although, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, awarding Buatsi just one round.
The victor progresses, but with the likes of power puncher Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - based on this performance - still seems difficult.
Hatton Memorial Inspires Manchester Derby Contest
In the secondary fight, Lyndon Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester battle to capture the continental championship.
The arena fell silent for a deeply poignant tribute before the fight as ten bells sounded in honor of local hero Hatton, who passed away aged 46 in September.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the concluding sound ended, the quiet transitioned to a roar of "there's just one Ricky Hatton".
The competition during the bout matched the sentiment. Arthur was sent to the canvas by a significant blow directly to the chin in the early round, standing uncertainly to his position on the eight count.
But the traditional red equipment of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was damaged soon, noticeable damage developing under his eye as the duo exchanged hard punches.
Rea, 27, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the action seldom decreased over twelve rounds.
Arthur barely secured the decision with official scores of 114-114, 115-113 and 115-112, but both fighters were relentless and courageous, all the qualities their inspiration Hatton represented.
