UK light-heavyweight Buatsi made a winning yet underwhelming beginning to his career under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a tight 10-round bout at the Manchester venue.
But the challenger landed significant shots, connecting with powerful clean blows in a match where the techniques never quite clicked, with constant grabbing spoiling the action.
The officials scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my greatest display but how do champions respond? They win," the victor said in the arena as he was greeted with disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to earn a twentieth professional win.
Various analysts believed the challenger, thirty-one, deserved the decision but the British boxer experienced the second setback of his 28-fight career.
The Champion Earns Triumph in Slow Affair
His career development has slowed in recent times through contract problems and extended periods of inactivity.
Previously predicted as the next star of the British fight scene, he now stands trying to achieve expectations - perhaps in what appears to be a last chance - under fresh management.
He began cautiously, with the two boxers prepared to be aggressive in a calculated initial rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in 2022 after breaking his hand during the bout, was participating in his second bout at light heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who worked behind a solid defense to narrowly win the better periods.
The crowd's patience wore thin during frequent holding, with Parker slipping to the canvas various instances during grappling.
Parker closed well, but several stanzas were difficult to score. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just a single round.
The victor moves on, but with the presence of power puncher David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Homage Inspires Manchester Derby Battle
In the secondary fight, Arthur beat Bradley Rea by split-decision in a excellent all-Manchester fight to secure the European light-heavyweight title.
The arena fell silent for a profoundly moving memorial before the fight as a bell ceremony sounded in memory of Manchester's own Ricky Hatton, who died aged 46 in last month.
It was the premier televised boxing event in the urban center since Hatton's passing. As the concluding sound faded, the silence transitioned to a chant of "only one Ricky Hatton".
The fighting within the ring equaled the sentiment. Arthur was knocked down by a left hook squarely on the chin in the early round, getting up unsteadily to his feet on the eight count.
But the traditional red equipment of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was damaged soon, noticeable damage forming under his eye as the fighters exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the pace rarely dropped over twelve rounds.
Arthur edged the verdict with judges scorecards of draw, close margin and 115-112, but both fighters were relentless and brave, everything their inspiration Hatton embodied.
