UK light-heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a competitive 10-round contest at the boxing arena.
But Parker found success, delivering effective clean blows in a match where the approaches didn't complement each other, with frequent clinching marring the fight.
The officials scored it 96-94 for to the winner, with the final judge a 95-95.
"It wasn't my best performance but how do champions respond? They win," Buatsi said in the arena as he was faced disapproval from the audience.
The Londoner bounced back after his maiden career setback - an memorable fight with his previous opponent in last winter - to secure a 20th pro success.
Several boxing experts believed the challenger, thirty-one, should have been awarded the decision but the Derbyshire fighter experienced the second defeat of his 28-fight professional journey.
The Champion Earns Triumph in Uneventful Encounter
The fighter's advancement has slowed in recent years through management issues and long spells of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to achieve expectations - possibly in what seems like a last chance - under fresh management.
He began cautiously, with neither fighter willing to overcommit in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was competing in only his second bout at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, making life awkward for the favorite, who operated with a tight guard to barely take the more effective rounds.
The crowd's patience decreased amid frequent holding, with the challenger going down multiple occasions during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. Nevertheless, previous titleholder Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the presence of power puncher David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Homage Fuels Local Rivalry Battle
In the co-main event, Arthur overcame Rea by split-decision in a outstanding local rivalry contest to secure the European light heavyweight championship.
The arena fell silent for a profoundly moving homage before the fight as a bell ceremony tolled in honor of the city's native Ricky Hatton, who died aged 46 in last month.
It was the initial significant broadcast fight night in the location since Hatton's death. As the last bell ended, the stillness transitioned to a chant of "there's just one Hatton".
The competition within the ring matched the emotion. The eventual winner was knocked down by a powerful punch squarely on the jaw in the early round, getting up unsteadily to his footing on the referee's count.
But the traditional red equipment of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was marked up quickly, noticeable damage forming under his orbital area as the duo landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with powerful upward punches as the intensity rarely dropped over the full distance.
Arthur narrowly won the result with judges scorecards of draw, 115-113 and wider gap, but each competitor were relentless and brave, everything their hero Hatton embodied.
