UK light heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive ten-round fight at the Manchester venue.
But the challenger found success, connecting with powerful single shots in a fight where the techniques didn't complement each other, with excessive holding spoiling the action.
Two judges judged it 96-94 to Buatsi, with the final judge a 95-95.
"It wasn't my best performance but what defines champions? They succeed," the victor stated in the ring as he was greeted with boos from the audience.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts believed Parker, 31, deserved the win but the British boxer experienced the second defeat of his 28-bout professional journey.
Buatsi Claims Victory in Slow Affair
Buatsi's progress has plateaued in recent years through promotional disputes and long spells of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to achieve expectations - possibly in what appears to be a last chance - under new promotional backing.
He began cautiously, with the two boxers prepared to be aggressive in a cagey early stages.
Parker, whose sole prior loss came at the lower weight class against John Ryder in 2022 after damaging his hand mid-fight, was making just his second bout at the higher weight class.
By the halfway stage, Parker had kept it close, making life awkward for the favorite, who utilized a tight guard to barely take the more effective periods.
The crowd's patience decreased during constant clinching, with the challenger falling to the floor multiple occasions during clinches.
The underdog ended stronger, but many rounds were hard to judge. However, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, giving Buatsi just one round.
The victor progresses, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Memorial Inspires Manchester Derby Contest
In the co-main event, Arthur beat Rea by divided decision in a terrific local rivalry fight to capture the European light heavyweight title.
The stadium grew hushed for a deeply poignant tribute prior to the bout as a bell ceremony tolled in memory of the city's native Hatton, who died 46 years old in last month.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the last bell disappeared, the stillness transitioned to a shout of "there's just one Ricky Hatton".
The competition during the bout reflected the emotion. Arthur was sent to the canvas by a powerful punch squarely on the chin in the second round, getting up unsteadily to his footing on the referee's count.
But the traditional red equipment of Arthur soon came forward again. From the other corner, the opponent - in rival City blue - was damaged early, heavy swelling forming under his eye as the duo exchanged punishing blows.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action seldom decreased over the full distance.
The victor narrowly won the decision with judges scorecards of even score, close margin and wider gap, but both fighters were relentless and full of heart, all the qualities their idol Hatton embodied.
