UK light-heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a majority decision in a close 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective single shots in a contest where the styles never quite clicked, with constant grabbing marring the fight.
The officials scored it 96-94 to the winner, with the final judge a even score.
"It wasn't my greatest display but how do champions respond? They win," Buatsi stated in the arena as he was faced disapproval from the spectators.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Various analysts felt the challenger, thirty-one, should have been awarded the decision but the contender endured the second defeat of his 28-match professional journey.
Buatsi Secures Win in Uneventful Match
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now finds himself trying to realize his potential - possibly in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with the two boxers ready to take risks in a tentative opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand in the contest, was competing in only his second bout at the higher weight class.
By the halfway stage, Parker had kept it close, causing problems for Buatsi, who worked behind a solid defense to edge the cleaner rounds.
The spectators' acceptance wore thin amid frequent holding, with Parker falling to the floor various instances during clinches.
Parker finished the stronger, but several stanzas were hard to judge. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi moves on, but with the presence of heavy hitter Benavidez, and Russian star Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Hatton Memorial Fuels Manchester Derby Contest
In the secondary fight, Arthur defeated Rea by close verdict in a terrific all-Manchester battle to win the European light-heavyweight belt.
The arena became quiet for a deeply poignant tribute ahead of the contest as a bell ceremony rang in remembrance of the city's native Ricky Hatton, who died at age 46 in recently.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the concluding sound disappeared, the stillness transitioned to a chant of "there's just one Ricky Hatton".
The action during the bout equaled the emotion. The eventual winner was floored by a left hook directly to the face in the second round, getting up unsteadily to his footing on the referee's count.
But the traditional red equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was marked up soon, heavy swelling developing under his face as the fighters landed powerful shots.
The challenger, 27, landed power punches but the champion, 34, fought fire with fire with effective uppercuts as the pace hardly diminished over the full distance.
Arthur barely secured the verdict with official scores of even score, close margin and 115-112, but both fighters were persistent and brave, all the qualities their inspiration Hatton embodied.
