UK light-heavyweight Joshua Buatsi earned a win yet disappointing start to his career under recent management with a unanimous decision 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 Co-op Live Arena.
But the challenger had his moments, delivering effective clean blows in a match where the approaches failed to mesh, with constant grabbing marring the contest.
Two judges had it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my greatest performance but how do champions respond? They win," Buatsi stated in the ringside as he was met by boos from the spectators.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts felt the challenger, 31, should have been awarded the decision but the contender endured the second defeat of his 28-bout professional journey.
The Champion Earns Triumph in Dull Encounter
The fighter's advancement has stalled in recent times through contract problems and extended periods of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors willing to take risks in a tentative early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second bout at light heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for Buatsi, who operated with a protective stance to narrowly win the cleaner stanzas.
The crowd's patience wore thin amid frequent holding, with Parker slipping to the canvas multiple occasions during close exchanges.
Parker closed well, but multiple periods were difficult to score. Although, former world champion the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor advances, but with the presence of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Memorial Motivates All-Manchester Battle
In the secondary fight, Arthur overcame Bradley Rea by split-decision in a excellent local rivalry fight to secure the European light heavyweight championship.
The venue grew hushed for a deeply poignant memorial before the fight as 10 bells rang in memory of local hero Ricky Hatton, who succumbed 46 years old in September.
It was the first major televised fight night in the urban center since Hatton's passing. As the last bell ended, the quiet gave way to a roar of "only one Hatton".
The competition within the ring matched the emotion. The eventual winner was sent to the canvas by a powerful punch squarely on the chin in the second round, rising shakily to his feet on the count of eight.
But the traditional red equipment of the fighter soon pressed ahead again. Across the ring, the opponent - in competitive blue - was injured quickly, significant bruising appearing under his orbital area as the pair exchanged punishing blows.
The challenger, 27, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the intensity seldom decreased over the full distance.
Arthur edged the result with scoring tallies of draw, 115-113 and wider gap, but the two athletes were relentless and brave, all the qualities their idol Hatton represented.
