British light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a split decision in a tight ten-round bout at the Manchester venue.
But the challenger found success, delivering effective clean blows in a contest where the techniques failed to mesh, with excessive holding disrupting the contest.
The scoring judges scored it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my greatest showing but what defines champions? They win," the victor stated in the ring as he was met by disapproval from the audience.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to secure a 20th pro success.
Some ringside observers thought Parker, 31, merited the win but the Derbyshire fighter endured the second setback of his 28-bout professional journey.
Buatsi Claims Win in Slow Encounter
Buatsi's progress has slowed in recent years through contract problems and extended periods of inactivity.
Earlier forecast as the future of the British fight scene, he now finds himself trying to realize his potential - perhaps in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with the two boxers willing to overcommit in a tentative early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second fight at the higher weight class.
By the halfway stage, the underdog had made it competitive, making life awkward for Buatsi, who utilized a solid defense to narrowly win the better stanzas.
The spectators' acceptance decreased because of frequent holding, with Parker slipping to the canvas several times during clinches.
Parker ended stronger, but many rounds were challenging to assess. However, former world champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Memorial Motivates All-Manchester Fight
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a excellent Manchester vs Manchester battle to win the European light heavyweight title.
The arena became quiet for a profoundly moving memorial ahead of the contest as ten bells rang in remembrance of Manchester's own Ricky Hatton, who passed away aged 46 in recently.
It was the first major televised match card in the city since Hatton's passing. As the last bell faded, the silence gave way to a roar of "there's just one Ricky Hatton".
The competition inside the ropes equaled the sentiment. The eventual winner was floored by a significant blow squarely on the face in the second round, standing uncertainly to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon pressed ahead again. Across the ring, the opponent - in opposing blue - was marked up soon, heavy swelling appearing under his face as the pair landed punishing blows.
Rea, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over 12 rounds.
The victor edged the decision with judges scorecards of even score, 115-113 and clearer margin, but the two athletes were determined and full of heart, everything their hero the legend represented.
