British light heavyweight Joshua Buatsi made a winning yet disappointing debut to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a majority decision in a close ten-round fight at the boxing arena.
But Parker found success, connecting with powerful single shots in a contest where the techniques never quite clicked, with excessive holding disrupting the action.
The officials scored it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my best performance but what defines champions? They prevail," the victor commented in the arena as he was met by boos from the audience.
The British fighter bounced back after his first professional defeat - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts thought the challenger, 31, deserved the decision but the Derbyshire fighter experienced the second setback of his 28-match professional journey.
The Champion Secures Win in Uneventful Match
The fighter's advancement has slowed in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the future of British boxing, he now stands trying to achieve expectations - maybe in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with both competitors prepared to overcommit in a calculated initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in 2022 after damaging his hand during the bout, was participating in his second appearance at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for the favorite, who utilized a protective stance to narrowly win the more effective stanzas.
The crowd's patience decreased amid constant clinching, with Parker going down various instances during clinches.
Parker closed well, but multiple periods were challenging to assess. Although, ex-champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - judging by this showing - still appears challenging.
Hatton Memorial Motivates Local Rivalry Battle
In the co-main event, Arthur defeated Bradley Rea by divided decision in a outstanding Manchester vs Manchester contest to win the continental belt.
The arena became quiet for a profoundly moving memorial prior to the bout as ten bells rang in remembrance of local hero Ricky Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the final chime disappeared, the silence became a shout of "only one Ricky Hatton".
The action inside the ropes matched the emotion. Arthur was knocked down by a significant blow flush on the jaw in the initial stage, standing uncertainly to his position on the eight count.
But the red-colored attire of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was marked up soon, noticeable damage appearing under his orbital area as the fighters landed hard punches.
Rea, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the action seldom decreased over the full distance.
The victor narrowly won the verdict with official scores of draw, 115-113 and clearer margin, but both fighters were persistent and full of heart, all the qualities their inspiration the legend stood for.
