British light-heavyweight Joshua Buatsi secured a victory yet unimpressive start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a majority decision in a tight 10-round bout at the Co-op Live Arena.
But Parker had his moments, connecting with powerful clean blows in a contest where the approaches didn't complement each other, with excessive holding spoiling the contest.
The officials judged it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest showing but what defines champions? They win," the victor stated in the ringside as he was met by disapproval from the audience.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Some ringside observers believed the challenger, thirty-one, merited the decision but the contender experienced the second defeat of his 28-bout career.
Buatsi Claims Win in Dull Match
Buatsi's progress has slowed in the past few years through contract problems and considerable time of lack of fights.
Previously predicted 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 neither fighter willing to be aggressive in a cagey early stages.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who utilized a solid defense to edge the cleaner periods.
The spectators' acceptance wore thin amid regular grabbing, with the challenger slipping to the canvas several times during grappling.
Parker closed well, but multiple periods were difficult to score. However, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
The victor advances, but with the presence of hard hitter David Benavidez, and Russian champion Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Hatton Tribute Fuels Local Rivalry Battle
In the co-main event, Arthur beat Rea by split-decision in a outstanding all-Manchester fight to capture the continental title.
The arena grew hushed for a deeply poignant memorial ahead of the contest as 10 bells sounded in honor of the city's native Ricky Hatton, who passed away aged 46 in September.
It was the first major televised fight night in the city since Hatton's death. As the last bell faded, the silence became a chant of "there's just one Ricky Hatton".
The competition during the bout matched the emotion. Arthur was sent to the canvas by a powerful punch flush on the jaw in the initial stage, standing uncertainly to his feet on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was injured early, significant bruising appearing under his face as the duo landed powerful shots.
Rea, 27, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the pace hardly diminished over 12 rounds.
Arthur barely secured the verdict with official scores of 114-114, close margin and 115-112, but the two athletes were persistent and brave, everything their idol Hatton embodied.
