UK light-heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a close ten-round fight at the Manchester venue.
But Parker had his moments, delivering effective single shots in a fight where the styles never quite clicked, with excessive holding disrupting the contest.
Two judges scored it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my best showing but how do champions respond? They succeed," Buatsi said in the ringside as he was faced boos from the audience.
The British fighter returned to winning ways after his initial pro loss - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Several boxing experts felt the challenger, thirty-one, deserved the win but the Derbyshire fighter suffered the second defeat of his 28-fight career.
The Champion Secures Win in Dull Match
Buatsi's progress has slowed in the past few years through promotional disputes and considerable time of lack of fights.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what appears to be a last chance - under fresh management.
He started carefully, with the two boxers ready to overcommit in a tentative initial rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in 2022 after damaging his hand in the contest, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a tight guard to narrowly win the more effective stanzas.
The crowd's patience wore thin during regular grabbing, with the challenger going down multiple occasions during close exchanges.
Parker ended stronger, but many rounds were hard to judge. However, former world champion Carl Frampton - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Hatton Homage Fuels Manchester Derby Battle
In the secondary fight, Arthur overcame Bradley Rea by close verdict in a outstanding local rivalry battle to secure the European light heavyweight championship.
The venue grew hushed for a extremely emotional memorial before the fight as a bell ceremony sounded in honor of Manchester's own Hatton, who succumbed 46 years old in September.
It was the first major televised match card in the urban center since Hatton's passing. As the concluding sound faded, the quiet became a chant of "there's only one Hatton".
The competition inside the ropes equaled the feeling. Arthur was sent to the canvas by a significant blow flush on the jaw in the initial stage, getting up unsteadily to his feet on the eight count.
But the red-colored attire of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was damaged early, significant bruising developing under his eye as the duo landed punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity hardly diminished over the full distance.
The victor edged the result with judges scorecards of even score, narrow lead and 115-112, but each competitor were determined and brave, everything their idol Hatton stood for.
