British light heavyweight Joshua Buatsi made a winning yet underwhelming start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a judges' verdict in a tight 10-round contest at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling single shots in a fight where the styles didn't complement each other, with excessive holding spoiling the action.
The officials judged it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest display but how do champions respond? They prevail," Buatsi commented in the ringside as he was met by disapproval from the spectators.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts believed Parker, thirty-one, should have been awarded the decision but the British boxer endured the second setback of his 28-match professional journey.
The Champion Claims Win in Slow Affair
The fighter's advancement has plateaued in recent years through promotional disputes and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to realize his potential - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with both competitors ready to take risks in a tentative initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, causing problems for the favorite, who utilized a protective stance to barely take the better periods.
The crowd's patience decreased because of constant clinching, with the challenger falling to the floor several times during grappling.
Parker finished the stronger, but multiple periods were hard to judge. However, former world champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just a single round.
Buatsi progresses, but with the caliber of hard hitter Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Homage Motivates Local Rivalry Contest
In the co-main event, Arthur defeated Bradley Rea by close verdict in a terrific Manchester vs Manchester battle to win the European light-heavyweight championship.
The venue became quiet for a profoundly moving homage before the fight as a bell ceremony rang in memory of local hero Hatton, who passed away aged 46 in September.
It was the first major televised match card in the city since the passing of Hatton. As the concluding sound ended, the quiet gave way to a chant of "only one Hatton".
The action during the bout reflected the emotion. Arthur was floored by a significant blow squarely on the jaw in the second round, getting up unsteadily to his position on the referee's count.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, Rea - in competitive blue - was damaged quickly, significant bruising appearing under his orbital area as the duo traded powerful shots.
The challenger, 27, connected with strong blows but Arthur, thirty-four, matched the intensity with effective uppercuts as the intensity seldom decreased over twelve rounds.
The victor narrowly won the decision with official scores of draw, narrow lead and 115-112, but both fighters were relentless and brave, all the qualities their hero the legend represented.
