UK light heavyweight Buatsi earned a win yet disappointing debut to life under recent management with a points victory over Zach Parker in Manchester.
The Olympic medal winner's work rate likely gained him a judges' verdict in a close ten-round fight at the Co-op Live Arena.
But Parker landed significant shots, landing some telling clean blows in a fight where the techniques didn't complement each other, with frequent clinching spoiling the action.
The officials scored it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best performance but what defines champions? They prevail," Buatsi commented in the ringside as he was faced disapproval from the crowd.
The British fighter got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to earn a 20th pro success.
Several boxing experts felt Parker, 31, merited the decision but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
The Champion Earns Victory in Uneventful Match
The fighter's advancement has plateaued in the past few years through management issues and long spells of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to realize his potential - possibly in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter prepared to be aggressive in a cagey initial rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand in the contest, was participating in his second fight at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who utilized a solid defense to narrowly win the cleaner rounds.
The crowd's patience decreased because of regular grabbing, with Parker slipping to the canvas multiple occasions during clinches.
Parker finished the stronger, but many rounds were hard to judge. Although, previous titleholder Carl Frampton - working with Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Tribute Inspires Local Rivalry Battle
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding Manchester vs Manchester contest to secure the European light heavyweight title.
The stadium fell silent for a profoundly moving memorial before the fight as 10 bells rang in remembrance of local hero Hatton, who died aged 46 in September.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the final chime ended, the quiet transitioned to a chant of "there's just one Hatton".
The competition within the ring reflected the feeling. The eventual winner was sent to the canvas by a significant blow squarely on the face in the early round, rising shakily to his position on the referee's count.
But the red-colored equipment of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was damaged early, significant bruising appearing under his orbital area as the duo traded hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action seldom decreased over the full distance.
Arthur narrowly won the result with scoring tallies of 114-114, narrow lead and clearer margin, but both fighters were relentless and courageous, everything their hero Hatton stood for.
