UK light-heavyweight Buatsi made a winning yet underwhelming start to his career under recent management with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a majority decision in a close 10-round fight at the boxing arena.
But Parker found success, delivering effective individual punches in a fight where the approaches failed to mesh, with constant grabbing marring the contest.
Two judges judged it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They win," the victor stated in the arena as he was greeted with boos from the crowd.
The Londoner bounced back after his first professional defeat - an thrilling contest with Callum Smith in February - to claim a 20th pro success.
Several boxing experts thought the challenger, 31, should have been awarded the victory but the contender endured the second defeat of his 28-match career.
Buatsi Secures Win in Slow Affair
The fighter's advancement has slowed in the past few years through promotional disputes and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to achieve expectations - maybe in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with both competitors willing to be aggressive in a calculated early stages.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand in the contest, was participating in his second fight at light-heavyweight.
By the middle rounds, Parker had stayed in contention, causing problems for the favorite, who utilized a protective stance to narrowly win the better rounds.
The spectators' acceptance diminished during constant clinching, with the challenger falling to the floor multiple occasions during clinches.
Parker ended stronger, but multiple periods were difficult to score. However, ex-champion the boxing analyst - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just a single round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still looks steep.
Hatton Homage Fuels Manchester Derby Contest
In the secondary fight, Lyndon Arthur overcame Rea by divided decision in a terrific local rivalry contest to win the continental belt.
The arena fell silent for a deeply poignant homage before the fight as a bell ceremony rang in memory of local hero Ricky Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the concluding sound ended, the silence transitioned to a chant of "there's just one Hatton".
The competition during the bout matched the sentiment. The eventual winner was floored by a left hook directly to the face in the initial stage, getting up unsteadily to his position on the eight count.
But the Manchester United-red shorts of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was damaged soon, significant bruising developing under his face as the fighters traded punishing blows.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the intensity seldom decreased over twelve rounds.
Arthur barely secured the verdict with judges scorecards of 114-114, 115-113 and 115-112, but the two athletes were relentless and brave, everything their inspiration the legend stood for.
