British light-heavyweight Joshua Buatsi earned a win yet underwhelming start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a majority decision in a close ten-round fight at the Manchester venue.
But the challenger landed significant shots, connecting with powerful single shots in a match where the techniques failed to mesh, with constant grabbing marring the fight.
The officials had it 96-94 for to the winner, with the third a 95-95.
"It wasn't my best display but what defines champions? They succeed," Buatsi said in the ringside as he was met by disapproval from the crowd.
The Londoner bounced back after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a 20th career victory.
Some ringside observers believed Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter suffered the second defeat of his 28-match professional journey.
The Champion Secures Triumph in Slow Encounter
Buatsi's progress has slowed in the past few years through contract problems and considerable time of inactivity.
Earlier forecast as the next star of British boxing, he now finds himself trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with the two boxers willing to overcommit in a tentative early stages.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second fight at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who worked behind a solid defense to edge the cleaner periods.
The spectators' acceptance wore thin during constant clinching, with the challenger slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but many rounds were hard to judge. Although, previous titleholder the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi moves on, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Tribute Fuels Local Rivalry Fight
In the secondary fight, Arthur defeated Bradley Rea by split-decision in a excellent local rivalry contest to secure the European light-heavyweight title.
The venue fell silent for a deeply poignant memorial ahead of the contest as 10 bells sounded in memory of Manchester's own Hatton, who passed away at age 46 in last month.
It was the premier televised fight night in the city since the passing of Hatton. As the concluding sound disappeared, the quiet gave way to a chant of "there's just one Hatton".
The fighting within the ring equaled the feeling. Arthur was knocked down by a powerful punch flush on the jaw in the initial stage, getting up unsteadily to his position on the referee's count.
But the red-colored equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in rival City blue - was injured quickly, significant bruising forming under his orbital area as the fighters exchanged powerful shots.
Rea, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the action seldom decreased over the full distance.
The victor barely secured the result with official scores of draw, narrow lead and clearer margin, but each competitor were determined and courageous, all the qualities their hero the legend stood for.
