UK light-heavyweight Joshua Buatsi secured a victory yet unimpressive start to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a tight ten-round fight at the Manchester venue.
But Parker had his moments, delivering effective single shots in a fight where the styles failed to mesh, with constant grabbing marring the contest.
Two judges scored it 96-94 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 commented in the ring as he was met by disapproval from the crowd.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers thought the challenger, thirty-one, should have been awarded the win but the contender experienced the second loss of his 28-bout professional journey.
The Champion Secures Victory in Dull Affair
His career development has stalled in recent times through promotional disputes and extended periods of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to fulfil that early promise - possibly in what seems like a last chance - under fresh management.
He opened tentatively, with the two boxers willing to be aggressive in a calculated initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after breaking his hand mid-fight, was competing in only his second appearance at light heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for the favorite, who operated with a tight guard to edge the cleaner periods.
The audience's tolerance diminished amid regular grabbing, with Parker slipping to the canvas various instances during grappling.
Parker finished the stronger, but several stanzas were difficult to score. Nevertheless, former world champion Carl Frampton - working with Dazn - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the presence of power puncher David Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Homage Inspires All-Manchester Contest
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a terrific Manchester vs Manchester contest to capture the European light-heavyweight championship.
The arena became quiet for a extremely emotional homage prior to the bout as ten bells rang in remembrance of local hero Ricky Hatton, who passed away aged 46 in September.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the final chime disappeared, the silence transitioned to a chant of "only one Ricky Hatton".
The fighting during the bout equaled the feeling. The eventual winner was floored by a left hook flush on the chin in the early round, getting up unsteadily to his footing on the referee's count.
But the traditional red shorts of Arthur soon pressed ahead again. From the other corner, Rea - in rival City blue - was injured early, heavy swelling forming under his orbital area as the pair landed powerful shots.
The challenger, twenty-seven, landed power punches but the champion, 34, matched the intensity with effective uppercuts as the intensity rarely dropped over 12 rounds.
The victor narrowly won the decision with official scores of even score, narrow lead and 115-112, but the two athletes were determined and brave, exactly what their hero Hatton stood for.
