British light heavyweight Joshua Buatsi earned a win yet unimpressive debut to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a competitive 10-round contest at the boxing arena.
But Parker found success, landing some telling clean blows in a fight where the styles failed to mesh, with frequent clinching disrupting the action.
The scoring judges had it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my best showing but what do champions do? They succeed," the victor commented in the arena as he was met by disapproval from the crowd.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Some ringside observers thought Parker, thirty-one, deserved the win but the contender experienced the second setback of his 28-match professional journey.
Buatsi Earns Triumph in Slow Encounter
Buatsi's progress has slowed in the past few years through promotional disputes and long spells of lack of fights.
Previously predicted as the rising talent of British boxing, he now finds himself trying to realize his potential - possibly in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors prepared to overcommit in a cagey early stages.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the fight's midpoint, the underdog had kept it close, causing problems for Buatsi, who operated with a solid defense to narrowly win the cleaner periods.
The audience's tolerance diminished during regular grabbing, with the challenger slipping to the canvas several times during close exchanges.
Parker ended stronger, but multiple periods were challenging to assess. Nevertheless, previous titleholder the boxing analyst - commentating on Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Hatton Tribute Inspires All-Manchester Fight
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a terrific local rivalry battle to secure the European light-heavyweight title.
The arena fell silent for a extremely emotional memorial before the fight as 10 bells rang in honor of the city's native Ricky Hatton, who died at age 46 in September.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the last bell ended, the quiet transitioned to a roar of "there's just one Ricky Hatton".
The action inside the ropes matched the emotion. The eventual winner was floored by a left hook directly to the face in the early round, rising shakily to his position on the referee's count.
But the traditional red attire of Arthur soon came forward again. From the other corner, Rea - in rival City blue - was injured quickly, noticeable damage forming under his eye as the pair exchanged punishing blows.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with effective uppercuts as the action seldom decreased over twelve rounds.
The victor edged the verdict with judges scorecards of draw, narrow lead and wider gap, but each competitor were relentless and brave, all the qualities their hero Hatton embodied.
