British light heavyweight Joshua Buatsi made a winning yet unimpressive debut to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a close 10-round bout at the Manchester venue.
But Parker landed significant shots, landing some telling individual punches in a match where the styles failed to mesh, with constant grabbing marring the action.
The scoring judges had it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my best showing but how do champions respond? They prevail," Buatsi stated in the ringside as he was greeted with boos from the crowd.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in February - to secure a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, merited the decision but the contender suffered the second defeat of his 28-fight career.
The Champion Secures Win in Slow Match
The fighter's advancement has stalled in recent times through contract problems and long spells of lack of fights.
Earlier forecast as the next star of the British fight scene, he now stands trying to realize his potential - possibly in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with neither fighter ready to be aggressive in a calculated initial rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was participating in his second bout at the higher weight class.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who utilized a tight guard to edge the cleaner stanzas.
The spectators' acceptance diminished because of frequent holding, with the challenger slipping to the canvas multiple occasions during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. However, ex-champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Tribute Inspires Manchester Derby Battle
In the supporting bout, Arthur overcame Rea by split-decision in a excellent Manchester vs Manchester fight to secure the continental belt.
The venue grew hushed for a extremely emotional tribute before the fight as a bell ceremony sounded in remembrance of the city's native Hatton, who died aged 46 in September.
It was the initial significant broadcast fight night in the urban center since Hatton's death. As the last bell ended, the stillness transitioned to a roar of "there's only one Hatton".
The action during the bout matched the sentiment. Arthur was floored by a significant blow squarely on the jaw in the initial stage, getting up unsteadily to his footing on the count of eight.
But the red-colored equipment of Arthur soon came forward again. Across the ring, Rea - in opposing blue - was damaged early, noticeable damage forming under his face as the duo exchanged punishing blows.
The challenger, 27, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the pace seldom decreased over the full distance.
The victor narrowly won the verdict with official scores of draw, narrow lead and clearer margin, but each competitor were determined and full of heart, exactly what their idol Hatton represented.
