UK light heavyweight Buatsi secured a victory yet unimpressive start to life under new promoters with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a split decision in a tight ten-round contest at the boxing arena.
But the challenger landed significant shots, delivering effective individual punches in a match where the styles never quite clicked, with excessive holding spoiling the fight.
Two judges scored it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest showing but what do champions do? They win," the victor said in the arena as he was met by disapproval from the crowd.
The British fighter returned to winning ways after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers felt Parker, 31, should have been awarded the win but the contender endured the second defeat of his 28-bout career.
The Champion Earns Victory in Dull Affair
His career development has slowed in the past few years through management issues and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to achieve expectations - possibly in what appears to be a last chance - under fresh management.
He opened tentatively, with neither fighter ready to be aggressive in a tentative initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after breaking his hand in the contest, was participating in his second appearance at the higher weight class.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who worked behind a solid defense to barely take the cleaner rounds.
The spectators' acceptance decreased during constant clinching, with Parker falling to the floor several times during close exchanges.
Parker ended stronger, but several stanzas were challenging to assess. Although, former world champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just only one stanza.
The victor advances, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Memorial Motivates All-Manchester Contest
In the supporting bout, Lyndon Arthur beat Rea by split-decision in a outstanding all-Manchester fight to win the European light heavyweight championship.
The stadium became quiet for a extremely emotional tribute ahead of the contest as a bell ceremony rang in memory of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the final chime disappeared, the stillness gave way to a shout of "only one Ricky Hatton".
The action during the bout reflected the sentiment. Arthur was sent to the canvas by a powerful punch flush on the jaw in the initial stage, standing uncertainly to his feet on the eight count.
But the traditional red attire of the fighter soon pressed ahead again. Across the ring, Rea - in rival City blue - was damaged soon, significant bruising developing under his eye as the duo traded hard punches.
Rea, 27, landed power punches but Arthur, thirty-four, responded in kind with effective uppercuts as the action seldom decreased over twelve rounds.
Arthur narrowly won the decision with official scores of even score, 115-113 and wider gap, but the two athletes were determined and full of heart, all the qualities their idol Hatton represented.
