British light heavyweight Joshua Buatsi secured a victory yet unimpressive start to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a close ten-round contest at the Manchester venue.
But Parker landed significant shots, landing some telling single shots in a contest where the techniques didn't complement each other, with frequent clinching spoiling the fight.
Two judges judged it 96-94 to Buatsi, with the third a even score.
"It wasn't my finest display but how do champions respond? They succeed," Buatsi stated in the ring as he was greeted with disapproval from the crowd.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to claim a 20th career victory.
Several boxing experts believed Parker, 31, deserved the win but the contender experienced the second setback of his 28-fight career.
The Champion Claims Win in Uneventful Match
The fighter's advancement has stalled in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, 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 breaking his hand mid-fight, was making just his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, creating difficulties for the favorite, who worked behind a tight guard to narrowly win the more effective stanzas.
The spectators' acceptance decreased because of regular grabbing, with the challenger slipping to the canvas multiple occasions during clinches.
The underdog ended stronger, but several stanzas were difficult to score. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, giving Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Homage Motivates Local Rivalry Contest
In the secondary fight, Arthur defeated Rea by split-decision in a terrific local rivalry battle to capture the continental title.
The arena fell silent for a extremely emotional tribute prior to the bout as ten bells sounded in memory of the city's native Ricky Hatton, who died aged 46 in recently.
It was the premier televised match card in the city since the passing of Hatton. As the last bell faded, the silence became a shout of "there's just one Hatton".
The competition within the ring equaled the feeling. The eventual winner was floored by a powerful punch squarely on the face in the early round, getting up unsteadily to his feet on the referee's count.
But the traditional red shorts of the fighter soon pressed ahead again. Across the ring, the opponent - in competitive blue - was marked up quickly, significant bruising forming under his eye as the fighters exchanged hard punches.
The challenger, 27, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur narrowly won the verdict with official scores of even score, narrow lead and clearer margin, but each competitor were persistent and courageous, everything their inspiration Hatton stood for.
