UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a split decision in a close ten-round bout at the Manchester venue.
But Parker landed significant shots, connecting with powerful individual punches in a fight where the techniques failed to mesh, with excessive holding marring the action.
The scoring judges had it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my best showing but what do champions do? They win," Buatsi stated in the arena as he was greeted with boos from the audience.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in February - to earn a 20th pro success.
Various analysts believed Parker, thirty-one, should have been awarded the win but the British boxer experienced the second setback of his 28-match career.
The Champion Claims Triumph in Uneventful Encounter
His career development has plateaued in recent times through management issues and long spells of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to achieve expectations - perhaps in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers prepared to take risks in a calculated early stages.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after damaging his hand during the bout, was making just his second fight at light-heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a protective stance to edge the cleaner stanzas.
The spectators' acceptance wore thin because of frequent holding, with the challenger slipping to the canvas several times during close exchanges.
Parker ended stronger, but multiple periods were difficult to score. Nevertheless, ex-champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just one round.
The victor progresses, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Memorial Motivates Manchester Derby Fight
In the secondary fight, Arthur overcame Rea by close verdict in a terrific Manchester vs Manchester contest to win the European light-heavyweight belt.
The stadium grew hushed for a deeply poignant memorial ahead of the contest as ten bells sounded in remembrance of Manchester's own Hatton, who passed away aged 46 in September.
It was the first major televised fight night in the location since Hatton's passing. As the final chime disappeared, the silence gave way to a shout of "there's just one Ricky Hatton".
The competition inside the ropes matched the emotion. Arthur was floored by a powerful punch squarely on the jaw in the initial stage, standing uncertainly to his position on the referee's count.
But the traditional red shorts of the fighter soon advanced again. On the opposite side, the opponent - in opposing blue - was injured soon, significant bruising appearing under his face as the pair traded powerful shots.
The challenger, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity hardly diminished over the full distance.
Arthur barely secured the decision with scoring tallies of draw, narrow lead and clearer margin, but the two athletes were determined and brave, all the qualities their idol Hatton embodied.
