UK light heavyweight Joshua Buatsi earned a win yet unimpressive debut to his career under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a split decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger had his moments, delivering effective individual punches in a contest where the approaches never quite clicked, with excessive holding disrupting the contest.
The officials judged it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my best performance but what defines champions? They succeed," the victor commented in the ring as he was greeted with boos from the audience.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to claim a 20th career victory.
Various analysts believed Parker, 31, merited the decision but the British boxer suffered the second loss of his 28-fight career.
Buatsi Secures Triumph in Uneventful Affair
The fighter's advancement has stalled in recent years through management issues and long spells of lack of fights.
Earlier forecast as the future of UK boxing, he now stands trying to fulfil that early promise - perhaps in what seems like a last chance - under recent support.
He began cautiously, with the two boxers willing to overcommit in a tentative early stages.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was making just his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for Buatsi, who worked behind a protective stance to barely take the more effective rounds.
The crowd's patience decreased during constant clinching, with Parker falling to the floor multiple occasions during close exchanges.
The underdog closed well, but several stanzas were difficult to score. Nevertheless, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just one round.
The victor progresses, but with the likes of hard hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - judging by this showing - still seems difficult.
Hatton Memorial Fuels Manchester Derby Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding Manchester vs Manchester contest to secure the continental title.
The venue became quiet for a extremely emotional homage ahead of the contest as a bell ceremony rang in remembrance of the city's native Hatton, who died aged 46 in recently.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the concluding sound disappeared, the stillness became a chant of "only one Ricky Hatton".
The action during the bout reflected the emotion. The eventual winner was knocked down by a significant blow flush on the face in the second round, rising shakily to his feet on the referee's count.
But the Manchester United-red equipment of the fighter soon advanced again. Across the ring, the opponent - in rival City blue - was injured early, significant bruising developing under his orbital area as the fighters landed powerful shots.
The challenger, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over twelve rounds.
Arthur edged the verdict with judges scorecards of draw, narrow lead and wider gap, but both fighters were persistent and courageous, all the qualities their hero the legend embodied.
