UK light-heavyweight Buatsi secured a victory yet disappointing start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a competitive 10-round fight at the Manchester venue.
But Parker had his moments, connecting with powerful single shots in a fight where the techniques never quite clicked, with frequent clinching disrupting the action.
The officials judged it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my finest showing but what do champions do? They win," the victor commented in the arena as he was met by boos from the audience.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Various analysts thought the challenger, thirty-one, should have been awarded the win but the contender experienced the second defeat of his 28-fight professional journey.
Buatsi Claims Triumph in Dull Affair
The fighter's advancement has stalled in recent times through contract problems and considerable time of lack of fights.
Once tipped as the future of British boxing, he now is positioned trying to achieve expectations - possibly in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter willing to take risks in a tentative opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after suffering a hand injury in the contest, was competing in only his second bout at light-heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who utilized a tight guard to narrowly win the more effective rounds.
The crowd's patience wore thin because of frequent holding, with the challenger slipping to the canvas several times during grappling.
Parker finished the stronger, but many rounds were challenging to assess. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - on this evidence - still appears challenging.
Hatton Tribute Motivates Local Rivalry Contest
In the co-main event, Arthur defeated Rea by split-decision in a terrific Manchester vs Manchester battle to capture the European light heavyweight championship.
The venue became quiet for a profoundly moving memorial before the fight as ten bells sounded in honor of Manchester's own Ricky Hatton, who succumbed at age 46 in last month.
It was the first major televised boxing event in the city since the passing of Hatton. As the concluding sound ended, the stillness transitioned to a roar of "only one Hatton".
The action within the ring reflected the emotion. The eventual winner was sent to the canvas by a powerful punch squarely on the jaw in the early round, getting up unsteadily to his footing on the referee's count.
But the red-colored attire of Arthur soon came forward again. From the other corner, the opponent - in rival City blue - was injured quickly, significant bruising appearing under his face as the duo traded punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the intensity seldom decreased over the full distance.
The victor narrowly won the verdict with scoring tallies of even score, close margin and 115-112, but both fighters were persistent and brave, everything their idol Hatton stood for.
