British light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a majority decision in a competitive 10-round fight at the boxing arena.
But Parker landed significant shots, connecting with powerful single shots in a match where the techniques failed to mesh, with excessive holding spoiling the action.
Two judges scored it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my greatest display but what do champions do? They win," the victor said in the ringside as he was met by boos from the audience.
The Londoner bounced back after his first professional defeat - an epic battle with his previous opponent in February - to secure a 20th career victory.
Various analysts felt Parker, 31, merited the win but the British boxer endured the second defeat of his 28-bout professional journey.
The Champion Earns Triumph in Uneventful Affair
The fighter's advancement has slowed in recent times through promotional disputes and long spells of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to achieve expectations - possibly in what appears to be a last chance - under new promotional backing.
He opened tentatively, with the two boxers ready to overcommit in a cagey opening few rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in 2022 after suffering a hand injury in the contest, was competing in only his second bout at the higher weight class.
By the halfway stage, Parker had stayed in contention, making life awkward for Buatsi, who utilized a protective stance to edge the more effective rounds.
The audience's tolerance decreased during frequent holding, with Parker going down several times during grappling.
The underdog ended stronger, but many rounds were challenging to assess. However, former world champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor progresses, but with the likes of power puncher Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Hatton Homage Inspires All-Manchester Contest
In the co-main event, Arthur beat Bradley Rea by close verdict in a outstanding Manchester vs Manchester contest to capture the European light heavyweight title.
The venue became quiet for a profoundly moving tribute before the fight as a bell ceremony tolled in honor of local hero Hatton, who died aged 46 in recently.
It was the premier televised boxing event in the city since the passing of Hatton. As the last bell disappeared, the quiet became a chant of "only one Ricky Hatton".
The fighting inside the ropes reflected the sentiment. Arthur was sent to the canvas by a significant blow flush on the face in the early round, rising shakily to his feet on the count of eight.
But the red-colored equipment of Arthur soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up quickly, noticeable damage developing under his eye as the fighters traded punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor edged the decision with judges scorecards of 114-114, narrow lead and wider gap, but both fighters were persistent and brave, everything their hero Hatton represented.
