British light-heavyweight Joshua Buatsi made a winning yet disappointing start to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close 10-round fight at the boxing arena.
But Parker found success, landing some telling single shots in a fight where the techniques failed to mesh, with constant grabbing spoiling the action.
The officials had it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my best showing but how do champions respond? They win," Buatsi stated in the ringside as he was greeted with boos from the crowd.
The Londoner got back to winning after his maiden career setback - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Some ringside observers felt Parker, thirty-one, should have been awarded the decision but the contender experienced the second loss of his 28-match professional journey.
Buatsi Earns Triumph in Slow Encounter
His career development has stalled in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to achieve expectations - maybe in what seems like a last chance - under recent support.
He began cautiously, with neither fighter ready to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second fight at light heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who operated with a tight guard to barely take the cleaner stanzas.
The crowd's patience decreased because of regular grabbing, with the challenger falling to the floor various instances during clinches.
The underdog closed well, but many rounds were challenging to assess. Nevertheless, former world champion Carl Frampton - working with Dazn - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - judging by this showing - still appears challenging.
Hatton Memorial Motivates All-Manchester Contest
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a terrific all-Manchester battle to secure the European light heavyweight title.
The venue grew hushed for a extremely emotional tribute prior to the bout as a bell ceremony tolled in remembrance of local hero Hatton, who succumbed aged 46 in September.
It was the first major televised fight night in the urban center since Hatton's death. As the concluding sound ended, the quiet gave way to a roar of "there's only one Ricky Hatton".
The competition within the ring equaled the emotion. The eventual winner was sent to the canvas by a powerful punch directly to the jaw in the early round, rising shakily to his feet on the count of eight.
But the Manchester United-red attire of Arthur soon came forward again. Across the ring, Rea - in opposing blue - was damaged quickly, heavy swelling appearing under his face as the pair landed powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the pace rarely dropped over twelve rounds.
Arthur narrowly won the verdict with judges scorecards of even score, narrow lead and wider gap, but the two athletes were relentless and brave, all the qualities their inspiration the legend represented.
