UK light heavyweight Buatsi made a winning yet disappointing start to life under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful single shots in a contest where the approaches didn't complement each other, with excessive holding disrupting the contest.
Two judges scored it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my best showing but how do champions respond? They succeed," the victor stated in the arena as he was met by negative reactions from the spectators.
The British fighter got back to winning after his maiden career setback - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers believed the challenger, 31, should have been awarded the win but the British boxer suffered the second loss of his 28-bout career.
Buatsi Claims Triumph in Slow Encounter
Buatsi's progress has slowed in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the future of British boxing, he now finds himself trying to achieve expectations - perhaps in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter prepared to take risks in a calculated early stages.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was making just his second bout at the higher weight class.
By the middle rounds, the underdog had stayed in contention, making life awkward for the favorite, who utilized a solid defense to barely take the cleaner stanzas.
The audience's tolerance diminished during constant clinching, with Parker falling to the floor several times during grappling.
Parker ended stronger, but many rounds were difficult to score. Nevertheless, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Homage Motivates All-Manchester Fight
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding local rivalry fight to capture the European light heavyweight belt.
The arena fell silent for a profoundly moving tribute ahead of the contest as ten bells tolled in memory of local hero Hatton, who died at age 46 in September.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the final chime ended, the silence became a shout of "there's just one Hatton".
The action within the ring matched the emotion. The eventual winner was knocked down by a significant blow flush on the chin in the early round, rising shakily to his footing on the count of eight.
But the traditional red equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was injured soon, heavy swelling appearing under his face as the fighters exchanged powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the action rarely dropped over the full distance.
Arthur narrowly won the decision with scoring tallies of 114-114, narrow lead and 115-112, but each competitor were determined and brave, all the qualities their hero Hatton stood for.
