UK light heavyweight Buatsi earned a win yet unimpressive start to life under fresh promotional backing 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 tight 10-round bout at the boxing arena.
But Parker found success, delivering effective clean blows in a match where the approaches never quite clicked, with constant grabbing marring the contest.
The officials scored it 96-94 in favor to the winner, with the third a even score.
"It wasn't my finest display but what do champions do? They succeed," the victor commented in the ring as he was greeted with disapproval from the spectators.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to secure a 20th career victory.
Several boxing experts felt Parker, thirty-one, should have been awarded the win but the Derbyshire fighter suffered the second defeat of his 28-fight professional journey.
Buatsi Earns Triumph in Uneventful Encounter
Buatsi's progress has slowed in recent years through contract problems and extended periods of lack of fights.
Once tipped as the future of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under recent support.
He started carefully, with neither fighter ready to take risks in a cagey early stages.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after suffering a hand injury during the bout, was participating in his second bout at light-heavyweight.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who operated with a protective stance to narrowly win the more effective stanzas.
The crowd's patience decreased amid constant clinching, with Parker slipping to the canvas multiple occasions during clinches.
Parker ended stronger, but multiple periods were hard to judge. However, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Memorial Motivates Local Rivalry Contest
In the supporting bout, Arthur beat Bradley Rea by split-decision in a excellent local rivalry contest to win the European light heavyweight belt.
The venue grew hushed for a profoundly moving tribute before the fight as ten bells rang in memory of the city's native Ricky Hatton, who passed away at age 46 in September.
It was the premier televised boxing event in the location since Hatton's death. As the final chime disappeared, the silence transitioned to a shout of "there's only one Hatton".
The competition within the ring reflected the feeling. The eventual winner was sent to the canvas by a left hook squarely on the face in the initial stage, getting up unsteadily to his footing on the eight count.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, Rea - in competitive blue - was injured soon, noticeable damage forming under his face as the pair landed powerful shots.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity hardly diminished over twelve rounds.
Arthur barely secured the decision with official scores of even score, close margin and 115-112, but each competitor were relentless and courageous, all the qualities their idol Hatton stood for.
