British light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a split decision in a competitive 10-round contest at the Manchester venue.
But Parker landed significant shots, landing some telling single shots in a fight where the approaches didn't complement each other, with excessive holding spoiling the fight.
Two judges had it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They win," the victor commented in the arena as he was met by negative reactions from the audience.
The British fighter bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers believed the challenger, 31, deserved the decision but the British boxer suffered the second loss of his 28-bout career.
Buatsi Secures Triumph in Dull Encounter
His career development has stalled in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the future of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with neither fighter willing to be aggressive in a calculated initial rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a solid defense to barely take the cleaner rounds.
The audience's tolerance diminished amid frequent holding, with Parker going down multiple occasions during grappling.
The underdog ended stronger, but multiple periods were challenging to assess. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the likes of power puncher Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - based on this performance - still appears challenging.
Hatton Homage Inspires Local Rivalry Fight
In the secondary fight, Arthur overcame Rea by divided decision in a excellent local rivalry fight to secure the European light-heavyweight title.
The stadium fell silent for a profoundly moving homage prior to the bout as a bell ceremony tolled in memory of the city's native Hatton, who succumbed 46 years old in September.
It was the first major televised fight night in the city since Hatton's death. As the concluding sound faded, the stillness transitioned to a chant of "there's only one Ricky Hatton".
The fighting during the bout reflected the sentiment. The eventual winner was floored by a left hook directly to the jaw in the early round, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red attire of the fighter soon pressed ahead again. Across the ring, the opponent - in competitive blue - was injured quickly, heavy swelling forming under his face as the pair landed punishing blows.
Rea, 27, delivered effective strikes but Arthur, 34, fought fire with fire with stinging uppercuts as the action rarely dropped over the full distance.
The victor narrowly won the verdict with official scores of 114-114, close margin and wider gap, but the two athletes were determined and brave, all the qualities their inspiration Hatton embodied.
