UK light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a tight 10-round bout at the Co-op Live Arena.
But the challenger found success, connecting with powerful individual punches in a contest where the approaches failed to mesh, with frequent clinching disrupting the contest.
The officials had it 96-94 to Buatsi, with the third a even score.
"It wasn't my best display but what do champions do? They win," the victor commented in the ringside as he was greeted with disapproval from the audience.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to earn a 20th pro success.
Various analysts felt the challenger, 31, merited the win but the British boxer experienced the second setback of his 28-match career.
Buatsi Secures Win in Slow Affair
His career development has slowed in recent times through contract problems and long spells of lack of fights.
Once tipped as the future of UK boxing, he now finds himself trying to realize his potential - possibly in what appears to be a ultimate opportunity - under fresh management.
He began cautiously, with the two boxers ready to be aggressive in a tentative early stages.
Parker, whose single earlier setback came at the lower weight class against his former opponent in 2022 after damaging his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for the favorite, who operated with a tight guard to barely take the better stanzas.
The audience's tolerance diminished during regular grabbing, with Parker going down various instances during grappling.
Parker closed well, but many rounds were hard to judge. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Tribute Fuels Local Rivalry Battle
In the co-main event, Arthur overcame Bradley Rea by divided decision in a excellent Manchester vs Manchester contest to secure the European light heavyweight championship.
The venue fell silent for a extremely emotional tribute prior to the bout as a bell ceremony rang in honor of the city's native Ricky Hatton, who passed away aged 46 in September.
It was the first major televised boxing event in the city since Hatton's passing. As the concluding sound faded, the stillness transitioned to a roar of "there's only one Hatton".
The fighting within the ring matched the feeling. Arthur was floored by a significant blow directly to the face in the second round, getting up unsteadily to his feet on the referee's count.
But the traditional red shorts of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was damaged soon, noticeable damage appearing under his eye as the duo traded hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the action hardly diminished over 12 rounds.
The victor barely secured the verdict with judges scorecards of 114-114, narrow lead and wider gap, but each competitor were relentless and full of heart, all the qualities their inspiration Hatton represented.
