UK light heavyweight Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a close ten-round bout at the boxing arena.
But Parker found success, landing some telling individual punches in a fight where the techniques didn't complement each other, with excessive holding spoiling the action.
Two judges had it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my greatest showing but what defines champions? They win," Buatsi commented in the ring as he was met by boos from the audience.
The British fighter bounced back after his first professional defeat - an thrilling contest with Callum Smith in February - to claim a 20th pro success.
Several boxing experts believed the challenger, 31, should have been awarded the decision but the British boxer suffered the second setback of his 28-bout career.
Buatsi Claims Win in Uneventful Affair
Buatsi's progress has slowed in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a last chance - under fresh management.
He opened tentatively, with both competitors 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 breaking his hand mid-fight, was competing in only his second fight at light heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for the favorite, who operated with a protective stance to narrowly win the cleaner periods.
The crowd's patience diminished amid frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
The underdog finished the stronger, but multiple periods were hard to judge. Although, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for Parker, giving Buatsi just one round.
The victor progresses, but with the likes of hard hitter David Benavidez, and Russian star Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Hatton Memorial Fuels Local Rivalry Battle
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a terrific local rivalry contest to secure the continental title.
The stadium fell silent for a profoundly moving homage before the fight as a bell ceremony rang in remembrance of Manchester's own Hatton, who died at age 46 in September.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the last bell faded, the silence transitioned to a chant of "there's just one Ricky Hatton".
The competition inside the ropes reflected the feeling. Arthur was sent to the canvas by a significant blow flush on the chin in the initial stage, rising shakily to his footing on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, the opponent - in competitive blue - was marked up quickly, noticeable damage developing under his orbital area as the fighters traded powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity seldom decreased over 12 rounds.
The victor narrowly won the result with judges scorecards of even score, 115-113 and 115-112, but the two athletes were determined and full of heart, exactly what their idol Hatton represented.
