British light-heavyweight Joshua Buatsi secured a victory yet underwhelming start to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a competitive ten-round contest at the boxing arena.
But the challenger landed significant shots, connecting with powerful individual punches in a match where the styles failed to mesh, with frequent clinching marring the action.
Two judges scored it 96-94 for to the winner, with the third a even score.
"It wasn't my greatest showing but what defines champions? They succeed," the victor said in the ringside as he was met by negative reactions from the spectators.
The Londoner got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to secure a 20th pro success.
Various analysts thought the challenger, 31, merited the win but the contender suffered the second setback of his 28-fight career.
Buatsi Earns Victory in Uneventful Encounter
Buatsi's progress has stalled in recent times through management issues and extended periods of inactivity.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a last chance - under recent support.
He opened tentatively, with the two boxers willing to overcommit in a tentative early stages.
Parker, whose only previous defeat came at super-middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was making just his second bout at the higher weight class.
By the halfway stage, the underdog had stayed in contention, causing problems for the favorite, who operated with a solid defense to edge the more effective rounds.
The audience's tolerance diminished during constant clinching, with the challenger slipping to the canvas several times during close exchanges.
The underdog ended stronger, but multiple periods were hard to judge. Nevertheless, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Memorial Motivates Local Rivalry Contest
In the co-main event, Arthur beat Bradley Rea by divided decision in a outstanding Manchester vs Manchester battle to capture the European light heavyweight title.
The venue grew hushed for a profoundly moving homage before the fight as a bell ceremony tolled in honor of local hero Hatton, who passed away at age 46 in last month.
It was the initial significant broadcast fight night in the urban center since Hatton's passing. As the final chime ended, the silence gave way to a shout of "there's only one Hatton".
The competition during the bout matched the emotion. Arthur was sent to the canvas by a significant blow squarely on the face in the initial stage, getting up unsteadily to his footing on the eight count.
But the red-colored shorts of the fighter soon advanced again. Across the ring, the opponent - in rival City blue - was marked up soon, noticeable damage appearing under his eye as the duo traded punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace hardly diminished over twelve rounds.
The victor narrowly won the decision with scoring tallies of draw, narrow lead and wider gap, but the two athletes were determined and courageous, exactly what their idol Hatton stood for.
