UK light-heavyweight Joshua Buatsi secured a victory yet disappointing beginning to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a close ten-round bout at the Manchester venue.
But the challenger found success, connecting with powerful individual punches in a contest where the styles didn't complement each other, with constant grabbing spoiling the action.
Two judges had it 96-94 for to Buatsi, 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 ring as he was faced boos from the audience.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to earn a 20th pro success.
Various analysts felt Parker, thirty-one, deserved the decision but the British boxer suffered the second loss of his 28-match professional journey.
The Champion Claims Triumph in Slow Match
Buatsi's progress has slowed in the past few years through contract problems and considerable time of lack of fights.
Previously predicted as the future of British boxing, he now stands trying to fulfil that early promise - perhaps in what appears to be a last chance - under new promotional backing.
He began cautiously, with neither fighter willing to take risks in a calculated opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after damaging his hand in the contest, was participating in his second appearance at light-heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for Buatsi, who utilized a solid defense to narrowly win the better rounds.
The audience's tolerance decreased because of frequent holding, with Parker falling to the floor multiple occasions during clinches.
The underdog ended stronger, but several stanzas were challenging to assess. However, former world champion the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, giving Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter Benavidez, and Russian champion Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Motivates Local Rivalry Fight
In the secondary fight, Arthur overcame Bradley Rea by split-decision in a excellent Manchester vs Manchester fight to capture the European light-heavyweight championship.
The arena fell silent for a extremely emotional memorial before the fight as ten bells sounded in remembrance of local hero Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast fight night in the city since Hatton's death. As the last bell ended, the quiet transitioned to a shout of "there's just one Ricky Hatton".
The competition within the ring matched the sentiment. The eventual winner was sent to the canvas by a powerful punch squarely on the chin in the initial stage, standing uncertainly to his feet on the eight count.
But the red-colored equipment of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was marked up soon, noticeable damage forming under his orbital area as the fighters exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the intensity rarely dropped over the full distance.
The victor narrowly won the verdict with judges scorecards of 114-114, close margin and wider gap, but both fighters were determined and courageous, everything their inspiration the legend stood for.
