UK light heavyweight Joshua Buatsi earned a win yet unimpressive debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a majority decision in a close 10-round bout at the Co-op Live Arena.
But the challenger had his moments, landing some telling single shots in a fight where the approaches failed to mesh, with constant grabbing disrupting the fight.
The officials judged it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest showing but what do champions do? They succeed," the victor said in the arena as he was met by boos from the audience.
The Londoner bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts believed the challenger, thirty-one, merited the win but the contender experienced the second loss of his 28-bout professional journey.
Buatsi Earns Win in Uneventful Encounter
The fighter's advancement has slowed in the past few years through contract problems and considerable time of inactivity.
Once tipped as the rising talent of UK boxing, he now is positioned trying to realize his potential - possibly in what feels like a last chance - under recent support.
He began cautiously, with the two boxers prepared to be aggressive in a tentative opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after damaging his hand mid-fight, was participating in his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for the favorite, who operated with a protective stance to barely take the better rounds.
The spectators' acceptance decreased during frequent holding, with Parker going down several times during grappling.
Parker ended stronger, but many rounds were hard to judge. However, former world champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Homage Motivates All-Manchester Contest
In the supporting bout, Arthur beat Rea by divided decision in a terrific Manchester vs Manchester contest to capture the European light heavyweight title.
The stadium fell silent for a extremely emotional homage before the fight as a bell ceremony sounded in honor of the city's native Ricky Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the last bell disappeared, the stillness transitioned to a shout of "only one Hatton".
The fighting inside the ropes matched the feeling. Arthur was sent to the canvas by a powerful punch directly to the chin in the early round, rising shakily to his position on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was injured early, noticeable damage forming under his eye as the duo exchanged powerful shots.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over the full distance.
The victor edged the result with judges scorecards of even score, 115-113 and clearer margin, but each competitor were persistent and courageous, exactly what their idol Hatton represented.
