British light-heavyweight Joshua Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a close ten-round contest at the Manchester venue.
But the challenger found success, delivering effective individual punches in a match where the techniques didn't complement each other, with frequent clinching disrupting the contest.
The scoring judges had it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest performance but what defines champions? They succeed," Buatsi commented in the ring as he was met by boos from the audience.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers felt Parker, 31, merited the victory but the British boxer suffered the second setback of his 28-match professional journey.
Buatsi Earns Victory in Dull Affair
His career development has plateaued in recent years through contract problems and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now is positioned trying to realize his potential - perhaps in what feels like a final roll of the dice - under recent support.
He opened tentatively, with both competitors ready to be aggressive in a cagey early stages.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was making just his second bout at light heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for the favorite, who worked behind a solid defense to barely take the cleaner periods.
The spectators' acceptance wore thin amid constant clinching, with the challenger going down multiple occasions during close exchanges.
Parker closed well, but multiple periods were hard to judge. Nevertheless, former world champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
The victor progresses, but with the presence of hard hitter David Benavidez, and Russian champion Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Hatton Homage Motivates All-Manchester Battle
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a outstanding Manchester vs Manchester battle to capture the European light heavyweight title.
The arena grew hushed for a deeply poignant tribute ahead of the contest as a bell ceremony rang in memory of local hero Hatton, who passed away at age 46 in last month.
It was the first major televised match card in the city since the passing of Hatton. As the last bell faded, the stillness transitioned to a roar of "there's only one Hatton".
The fighting within the ring equaled the emotion. Arthur was knocked down by a left hook directly to the jaw in the second round, getting up unsteadily to his feet on the count of eight.
But the red-colored attire of the fighter soon pressed ahead again. Across the ring, the opponent - in competitive blue - was marked up soon, heavy swelling developing under his orbital area as the duo exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action hardly diminished over twelve rounds.
Arthur narrowly won the verdict with official scores of draw, close margin and wider gap, but both fighters were relentless and full of heart, exactly what their inspiration Hatton embodied.
