British light-heavyweight Joshua Buatsi made a winning yet unimpressive debut to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a tight ten-round fight at the boxing arena.
But the challenger had his moments, delivering effective individual punches in a fight where the techniques failed to mesh, with excessive holding disrupting the action.
The scoring judges had it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my greatest display but what do champions do? They win," the victor commented in the ringside as he was met by disapproval from the crowd.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Several boxing experts felt the challenger, thirty-one, merited the win but the Derbyshire fighter experienced the second defeat of his 28-match professional journey.
The Champion Earns Triumph in Uneventful Match
His career development has stalled in recent times through management issues and long spells of lack of fights.
Previously predicted as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what seems like a last chance - under recent support.
He began cautiously, with neither fighter prepared to be aggressive in a cagey opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in 2022 after breaking his hand in the contest, was participating in his second appearance at the higher weight class.
By the middle rounds, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a protective stance to barely take the cleaner periods.
The spectators' acceptance decreased because of constant clinching, with the challenger falling to the floor various instances during clinches.
Parker closed well, but many rounds were hard to judge. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Hatton Memorial Motivates Local Rivalry Contest
In the supporting bout, Arthur beat Bradley Rea by split-decision in a outstanding local rivalry fight to win the continental championship.
The stadium fell silent for a deeply poignant memorial ahead of the contest as ten bells rang in remembrance of Manchester's own Ricky Hatton, who succumbed at age 46 in recently.
It was the first major televised match card in the location since the passing of Hatton. As the concluding sound ended, the quiet became a roar of "there's just one Ricky Hatton".
The fighting within the ring equaled the sentiment. The eventual winner was sent to the canvas by a left hook squarely on the chin in the second round, getting up unsteadily to his position on the eight count.
But the traditional red equipment of the fighter soon advanced again. On the opposite side, the opponent - in competitive blue - was injured soon, significant bruising appearing under his face as the pair exchanged powerful shots.
The challenger, twenty-seven, landed power punches but the champion, 34, matched the intensity with effective uppercuts as the intensity seldom decreased over twelve rounds.
Arthur barely secured the decision with judges scorecards of draw, narrow lead and clearer margin, but both fighters were determined and brave, everything their idol the legend stood for.
