UK light heavyweight Joshua Buatsi made a winning yet unimpressive start to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive 10-round bout at the Co-op Live Arena.
But Parker landed significant shots, delivering effective single shots in a fight where the approaches didn't complement each other, with constant grabbing disrupting the action.
The officials judged it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best display but how do champions respond? They win," the victor said in the ring as he was greeted with negative reactions from the crowd.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in February - to secure a 20th pro success.
Various analysts felt the challenger, 31, merited the win but the British boxer experienced the second defeat of his 28-bout career.
Buatsi Earns Triumph in Uneventful Match
The fighter's advancement has stalled in the past few years through promotional disputes and extended periods of lack of fights.
Previously predicted as the future of UK boxing, he now finds himself trying to realize his potential - maybe in what seems like a last chance - under fresh management.
He started carefully, with both competitors prepared to be aggressive in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was competing in only his second appearance at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a tight guard to narrowly win the more effective rounds.
The spectators' acceptance decreased because of frequent holding, with the challenger going down multiple occasions during grappling.
Parker closed well, but many rounds were difficult to score. Although, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just a single round.
The victor advances, but with the caliber of heavy hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Hatton Tribute Inspires Local Rivalry Contest
In the secondary fight, Arthur overcame Rea by split-decision in a excellent all-Manchester fight to win the European light-heavyweight championship.
The stadium became quiet for a profoundly moving homage ahead of the contest as 10 bells sounded in honor of the city's native Ricky Hatton, who died at age 46 in recently.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the last bell ended, the quiet transitioned to a chant of "there's just one Hatton".
The fighting inside the ropes reflected the emotion. The eventual winner was sent to the canvas by a significant blow squarely on the face in the initial stage, rising shakily to his position on the count of eight.
But the Manchester United-red attire of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was damaged early, heavy swelling appearing under his face as the duo exchanged punishing blows.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace seldom decreased over the full distance.
The victor barely secured the verdict with official scores of draw, 115-113 and clearer margin, but both fighters were persistent and brave, everything their inspiration the legend represented.
