UK light-heavyweight Buatsi earned a win yet disappointing start to life under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a majority decision in a close 10-round bout at the Co-op Live Arena.
But Parker had his moments, connecting with powerful individual punches in a fight where the techniques failed to mesh, with excessive holding spoiling the action.
The officials had it 96-94 for to the winner, with the third a even score.
"It wasn't my greatest showing but how do champions respond? They succeed," the victor said in the arena as he was met by negative reactions from the audience.
The British fighter bounced back after his first professional defeat - an memorable fight with Callum Smith in February - to claim a 20th career victory.
Some ringside observers believed Parker, thirty-one, should have been awarded the win but the British boxer endured the second setback of his 28-fight professional journey.
Buatsi Secures Triumph in Dull Encounter
Buatsi's progress has plateaued in recent times through promotional disputes and long spells of lack of fights.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter willing to be aggressive in a cagey initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was participating in his second bout at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who worked behind a tight guard to barely take the more effective stanzas.
The crowd's patience diminished during regular grabbing, with the challenger going down various instances during close exchanges.
Parker closed well, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - working with Dazn - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi advances, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Motivates Manchester Derby Battle
In the co-main event, Arthur defeated Bradley Rea by divided decision in a excellent Manchester vs Manchester fight to win the European light-heavyweight title.
The stadium became quiet for a deeply poignant homage prior to the bout as a bell ceremony rang in honor of Manchester's own Hatton, who passed away at age 46 in September.
It was the first major televised boxing event in the location since Hatton's passing. As the concluding sound faded, the quiet gave way to a shout of "there's just one Hatton".
The competition within the ring equaled the feeling. Arthur was floored by a significant blow directly to the face in the second round, rising shakily to his position on the referee's count.
But the red-colored shorts of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was injured soon, heavy swelling appearing under his face as the duo traded punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with effective uppercuts as the action rarely dropped over the full distance.
Arthur narrowly won the result with judges scorecards of draw, 115-113 and 115-112, but both fighters were persistent and courageous, exactly what their hero the legend embodied.
