British light-heavyweight Joshua Buatsi earned a win yet unimpressive debut to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a tight ten-round bout at the Manchester venue.
But Parker found success, connecting with powerful single shots in a contest where the techniques never quite clicked, with excessive holding spoiling the action.
The officials judged it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my best display but how do champions respond? They win," the victor stated in the arena as he was faced disapproval from the crowd.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers believed the challenger, 31, should have been awarded the decision but the contender suffered the second setback of his 28-fight career.
Buatsi Secures Victory in Uneventful Affair
The fighter's advancement has stalled in the past few years through promotional disputes and long spells of inactivity.
Previously predicted as the future of British boxing, he now finds himself trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter willing to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was making just his second appearance at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for the favorite, who utilized a protective stance to edge the more effective rounds.
The crowd's patience diminished amid frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
The underdog finished the stronger, but many rounds were challenging to assess. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, scoring for Buatsi just one round.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Hatton Homage Motivates Local Rivalry Battle
In the supporting bout, Arthur beat Rea by close verdict in a outstanding Manchester vs Manchester fight to capture the continental belt.
The arena became quiet for a deeply poignant homage before the fight as ten bells sounded in remembrance of Manchester's own Hatton, who succumbed aged 46 in September.
It was the first major televised match card in the urban center since the passing of Hatton. As the final chime ended, the silence gave way to a chant of "there's only one Ricky Hatton".
The action inside the ropes reflected the sentiment. Arthur was sent to the canvas by a left hook squarely on the face in the initial stage, getting up unsteadily to his feet on the count of eight.
But the traditional red equipment of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was damaged soon, noticeable damage appearing under his orbital area as the duo landed punishing blows.
The challenger, 27, delivered effective strikes but Arthur, 34, fought fire with fire with effective uppercuts as the action seldom decreased over 12 rounds.
Arthur narrowly won the decision with scoring tallies of even score, 115-113 and wider gap, but both fighters were relentless and full of heart, everything their inspiration Hatton embodied.
