UK light heavyweight Buatsi earned a win yet disappointing debut to his career under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a close ten-round bout at the Manchester venue.
But Parker had his moments, connecting with powerful individual punches in a match where the techniques never quite clicked, with excessive holding marring the contest.
The officials judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my best showing but how do champions respond? They succeed," Buatsi commented in the ringside as he was met by disapproval from the crowd.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts felt Parker, thirty-one, merited the decision but the British boxer experienced the second defeat of his 28-bout career.
Buatsi Secures Victory in Uneventful Affair
His career development has plateaued in recent years through management issues and considerable time of lack of fights.
Once tipped as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with neither fighter willing to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in 2022 after damaging his hand in the contest, was making just his second fight at light heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for the favorite, who operated with a tight guard to barely take the more effective periods.
The crowd's patience wore thin during frequent holding, with the challenger slipping to the canvas multiple occasions during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Homage Fuels All-Manchester Fight
In the co-main event, Lyndon Arthur beat Rea by split-decision in a outstanding all-Manchester fight to secure the continental championship.
The venue became quiet for a extremely emotional homage before the fight as 10 bells sounded in honor of the city's native Ricky Hatton, who succumbed 46 years old in recently.
It was the initial significant broadcast match card in the location since Hatton's death. As the final chime disappeared, the stillness became a roar of "only one Hatton".
The competition inside the ropes matched the emotion. Arthur was knocked down by a significant blow directly to the face in the second round, rising shakily to his position on the count of eight.
But the traditional red attire of Arthur soon came forward again. Across the ring, the opponent - in rival City blue - was marked up quickly, noticeable damage forming under his face as the pair landed powerful shots.
Rea, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with effective uppercuts as the action rarely dropped over the full distance.
The victor edged the result with official scores of 114-114, close margin and 115-112, but both fighters were relentless and courageous, all the qualities their inspiration Hatton stood for.
