UK light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a close 10-round contest at the Manchester venue.
But the challenger had his moments, connecting with powerful single shots in a fight where the styles failed to mesh, with constant grabbing disrupting the action.
The scoring judges had it 96-94 for to Buatsi, with the third a even score.
"It wasn't my finest performance but how do champions respond? They prevail," Buatsi commented in the ring as he was greeted with disapproval from the spectators.
The Londoner got back to winning after his first professional defeat - an thrilling contest with Callum Smith in February - to earn a 20th career victory.
Some ringside observers thought Parker, thirty-one, should have been awarded the victory but the British boxer experienced the second setback of his 28-bout career.
The Champion Secures Triumph in Dull Affair
His career development has plateaued in recent years through contract problems and long spells of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a last chance - under fresh management.
He began cautiously, with both competitors willing to take risks in a calculated opening few rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second bout at light heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for Buatsi, who worked behind a solid defense to narrowly win the more effective rounds.
The crowd's patience decreased amid regular grabbing, with the challenger falling to the floor several times during grappling.
Parker closed well, but multiple periods were difficult to score. Although, ex-champion the boxing analyst - commentating on Dazn - had it strongly leaning for Parker, scoring for Buatsi just one round.
The victor moves on, but with the likes of heavy hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Tribute Motivates All-Manchester Fight
In the co-main event, Arthur beat Bradley Rea by divided decision in a terrific all-Manchester battle to secure the European light-heavyweight title.
The stadium fell silent for a profoundly moving tribute ahead of the contest as 10 bells sounded in remembrance of Manchester's own Ricky Hatton, who succumbed 46 years old in recently.
It was the first major televised fight night in the urban center since the passing of Hatton. As the final chime disappeared, the quiet transitioned to a chant of "only one Hatton".
The action inside the ropes reflected the sentiment. The eventual winner was knocked down by a significant blow directly to the face in the second round, standing uncertainly to his footing on the referee's count.
But the Manchester United-red attire of the fighter soon came forward again. Across the ring, the opponent - in competitive blue - was injured early, significant bruising developing under his orbital area as the pair traded hard punches.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the intensity hardly diminished over 12 rounds.
Arthur edged the verdict with official scores of even score, close margin and 115-112, but the two athletes were persistent and brave, everything their idol Hatton represented.
