British light-heavyweight Joshua Buatsi earned a win yet underwhelming beginning to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a close 10-round bout at the boxing arena.
But Parker landed significant shots, connecting with powerful single shots in a match where the techniques didn't complement each other, with frequent clinching disrupting the action.
The officials had it 96-94 for to Buatsi, with the third a even score.
"It wasn't my finest showing but how do champions respond? They prevail," Buatsi said in the arena as he was faced disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to secure a 20th pro success.
Some ringside observers thought Parker, 31, merited the win but the Derbyshire fighter experienced the second loss of his 28-fight career.
Buatsi Claims Victory in Uneventful Affair
His career development has slowed in the past few years through contract problems and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now finds himself trying to achieve expectations - perhaps in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers ready to overcommit in a calculated initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, was making just his second fight at light heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for the favorite, who utilized a protective stance to barely take the better rounds.
The audience's tolerance wore thin during frequent holding, with Parker slipping to the canvas multiple occasions during clinches.
Parker finished the stronger, but multiple periods were difficult to score. Although, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, giving Buatsi just one round.
The victor advances, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Hatton Tribute Motivates All-Manchester Contest
In the supporting bout, Arthur beat Rea by split-decision in a terrific local rivalry contest to win the continental title.
The stadium became quiet for a extremely emotional tribute prior to the bout as a bell ceremony sounded in memory of Manchester's own Hatton, who succumbed at age 46 in September.
It was the premier televised boxing event in the location since the passing of Hatton. As the final chime ended, the silence gave way to a roar of "there's only one Hatton".
The fighting inside the ropes equaled the emotion. Arthur was knocked down by a significant blow squarely on the jaw in the initial stage, rising shakily to his position on the referee's count.
But the traditional red attire of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was injured quickly, significant bruising appearing under his face as the fighters exchanged powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the action seldom decreased over 12 rounds.
The victor edged the verdict with judges scorecards of even score, narrow lead and wider gap, but both fighters were determined and full of heart, all the qualities their inspiration the legend represented.
