British light heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, landing some telling clean blows in a match where the styles didn't complement each other, with excessive holding spoiling the contest.
Two judges scored it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my greatest performance but how do champions respond? They prevail," the victor said in the arena as he was faced negative reactions from the crowd.
The Londoner got back to winning after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts believed Parker, thirty-one, merited the decision but the Derbyshire fighter experienced the second defeat of his 28-bout career.
Buatsi Secures Win in Dull Affair
His career development has plateaued in recent times through contract problems and long spells of inactivity.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to realize his potential - possibly in what feels like a last chance - under fresh management.
He opened tentatively, with neither fighter ready to be aggressive in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after damaging his hand in the contest, was making just his second fight at light-heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who operated with a protective stance to barely take the more effective periods.
The audience's tolerance wore thin amid frequent holding, with the challenger going down various instances during grappling.
The underdog closed well, but many rounds were difficult to score. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor advances, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Memorial Motivates Local Rivalry Fight
In the supporting bout, Arthur beat Bradley Rea by close verdict in a outstanding Manchester vs Manchester contest to win the European light heavyweight belt.
The venue fell silent for a profoundly moving memorial ahead of the contest as 10 bells rang in remembrance of the city's native Hatton, who passed away 46 years old in September.
It was the first major televised match card in the location since Hatton's death. As the last bell faded, the stillness gave way to a chant of "only one Ricky Hatton".
The fighting during the bout reflected the feeling. The eventual winner was knocked down by a significant blow flush on the jaw in the second round, rising shakily to his footing on the count of eight.
But the Manchester United-red shorts of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was injured early, heavy swelling developing under his orbital area as the pair traded punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the intensity seldom decreased over 12 rounds.
The victor barely secured the decision with official scores of even score, 115-113 and 115-112, but each competitor were relentless and brave, all the qualities their inspiration Hatton stood for.
