UK light-heavyweight Buatsi secured a victory yet unimpressive start to his career under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a close 10-round fight at the Co-op Live Arena.
But Parker had his moments, delivering effective clean blows in a match where the approaches failed to mesh, with frequent clinching spoiling the fight.
The officials scored it 96-94 to the winner, with the third a even score.
"It wasn't my finest showing but what do champions do? They prevail," the victor said in the arena as he was met by negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Several boxing experts thought Parker, thirty-one, should have been awarded the win but the British boxer endured the second setback of his 28-bout career.
The Champion Secures Win in Slow Match
His career development has plateaued in recent times through promotional disputes and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under recent support.
He began cautiously, with neither fighter ready to take risks in a tentative initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand mid-fight, was making just his second appearance at the higher weight class.
By the halfway stage, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a protective stance to edge the better periods.
The spectators' acceptance wore thin amid constant clinching, with Parker falling to the floor multiple occasions during close exchanges.
Parker ended stronger, but several stanzas were hard to judge. However, previous titleholder the boxing analyst - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
The victor progresses, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Tribute Motivates Local Rivalry Fight
In the co-main event, Lyndon Arthur beat Rea by close verdict in a excellent local rivalry contest to capture the European light heavyweight belt.
The arena became quiet for a deeply poignant tribute ahead of the contest as ten bells rang in memory of the city's native Hatton, who succumbed aged 46 in recently.
It was the premier televised fight night in the location since Hatton's death. As the final chime disappeared, the silence gave way to a roar of "there's only one Ricky Hatton".
The competition during the bout equaled the emotion. Arthur was knocked down by a significant blow directly to the face in the second round, getting up unsteadily to his feet on the count of eight.
But the red-colored attire of the fighter soon advanced again. On the opposite side, the opponent - in rival City blue - was marked up early, heavy swelling developing under his orbital area as the fighters traded punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with effective uppercuts as the action rarely dropped over the full distance.
Arthur narrowly won the result with scoring tallies of draw, narrow lead and wider gap, but each competitor were persistent and courageous, everything their hero the legend represented.
