UK light heavyweight Joshua Buatsi secured a victory yet underwhelming start to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a close 10-round contest at the Manchester venue.
But Parker had his moments, connecting with powerful clean blows in a fight where the approaches never quite clicked, with constant grabbing disrupting the contest.
Two judges scored it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my finest performance but how do champions respond? They prevail," Buatsi said in the arena as he was met by negative reactions from the crowd.
The British fighter bounced back after his initial pro loss - an epic battle with his previous opponent in February - to earn a 20th career victory.
Several boxing experts felt the challenger, 31, should have been awarded the decision but the Derbyshire fighter endured the second setback of his 28-fight professional journey.
Buatsi Claims Triumph in Slow Match
Buatsi's progress has plateaued in recent years through management issues and long spells of lack of fights.
Once tipped as the next star of British boxing, he now stands trying to achieve expectations - perhaps in what feels like a last chance - under fresh management.
He started carefully, with both competitors prepared to take risks in a cagey early stages.
Parker, whose single earlier setback came at super-middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was competing in only his second appearance at light heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to edge the more effective rounds.
The audience's tolerance wore thin amid regular grabbing, with Parker going down multiple occasions during close exchanges.
The underdog closed well, but several stanzas were difficult to score. However, ex-champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Memorial Inspires Manchester Derby Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester contest to secure the European light-heavyweight championship.
The arena grew hushed for a deeply poignant tribute ahead of the contest as 10 bells tolled in honor of local hero Ricky Hatton, who succumbed at age 46 in September.
It was the premier televised fight night in the location since the passing of Hatton. As the last bell disappeared, the silence became a roar of "only one Ricky Hatton".
The competition within the ring reflected the sentiment. The eventual winner was sent to the canvas by a powerful punch directly to the chin in the second round, standing uncertainly to his position on the eight count.
But the traditional red attire of Arthur soon pressed ahead again. Across the ring, Rea - in rival City blue - was damaged early, heavy swelling appearing under his face as the fighters traded hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with stinging uppercuts as the intensity hardly diminished over the full distance.
Arthur edged the result with scoring tallies of even score, 115-113 and wider gap, but each competitor were relentless and full of heart, exactly what their hero the legend stood for.
