British light heavyweight Buatsi earned a win yet underwhelming beginning to his career under new promoters with a decision win over Zach Parker in Manchester.
The Olympic medal winner's activity level likely gained him a judges' verdict in a close 10-round fight at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful individual punches in a fight where the approaches never quite clicked, with excessive holding marring the action.
The officials judged it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my finest display but what defines champions? They win," Buatsi commented in the arena as he was faced boos from the spectators.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts believed Parker, 31, merited the victory but the British boxer endured the second setback of his 28-bout career.
Buatsi Earns Win in Slow Encounter
Buatsi's progress has slowed in the past few years through management issues and long spells of inactivity.
Earlier forecast as the next star of British boxing, he now stands trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers ready to take risks in a tentative opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for Buatsi, who utilized a protective stance to barely take the cleaner periods.
The spectators' acceptance diminished amid regular grabbing, with the challenger falling to the floor several times during grappling.
Parker closed well, but multiple periods were difficult to score. Although, previous titleholder the boxing analyst - working with the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
Buatsi moves on, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Memorial Fuels Local Rivalry Battle
In the secondary fight, Arthur overcame Rea by close verdict in a excellent all-Manchester battle to capture the continental belt.
The arena became quiet for a deeply poignant tribute prior to the bout as a bell ceremony tolled in remembrance of local hero Hatton, who passed away aged 46 in last month.
It was the first major televised boxing event in the location since the passing of Hatton. As the concluding sound disappeared, the stillness gave way to a chant of "there's only one Hatton".
The action during the bout reflected the emotion. Arthur was sent to the canvas by a left hook directly to the face in the early round, rising shakily to his position on the eight count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was damaged quickly, significant bruising developing under his eye as the fighters traded punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with powerful upward punches as the intensity seldom decreased over the full distance.
Arthur narrowly won the verdict with judges scorecards of draw, narrow lead and 115-112, but both fighters were persistent and brave, everything their idol the legend stood for.
