British light-heavyweight Buatsi secured a victory yet disappointing beginning to his career under new promoters with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a close ten-round contest at the boxing arena.
But the challenger had his moments, delivering effective single shots in a fight where the styles never quite clicked, with frequent clinching marring the action.
The officials judged it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my best display but how do champions respond? They prevail," Buatsi commented in the arena as he was greeted with disapproval from the spectators.
The Londoner bounced back after his first professional defeat - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Some ringside observers believed the challenger, thirty-one, should have been awarded the decision but the Derbyshire fighter experienced the second setback of his 28-match career.
The Champion Claims Victory in Slow Affair
The fighter's advancement has plateaued in recent years through contract problems and considerable time of inactivity.
Previously predicted as the next star of British boxing, he now is positioned trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under recent support.
He began cautiously, with neither fighter willing to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was participating in his second appearance at the higher weight class.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who utilized a tight guard to edge the better periods.
The crowd's patience diminished amid constant clinching, with Parker going down several times during clinches.
Parker ended stronger, but several stanzas were hard to judge. Nevertheless, previous titleholder the boxing analyst - commentating on Dazn - had it strongly leaning for Parker, giving Buatsi just a single round.
The victor advances, but with the likes of power puncher David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Battle
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a outstanding local rivalry contest to secure the European light heavyweight title.
The venue became quiet for a deeply poignant memorial ahead of the contest as ten bells tolled in remembrance of Manchester's own Ricky Hatton, who died aged 46 in last month.
It was the premier televised boxing event in the city since Hatton's death. As the final chime faded, the stillness became a chant of "only one Hatton".
The competition during the bout matched the emotion. The eventual winner was floored by a left hook directly to the face in the initial stage, getting up unsteadily to his position on the eight count.
But the red-colored equipment of the fighter soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was marked up soon, significant bruising developing under his eye as the duo landed powerful shots.
The challenger, 27, landed power punches but Arthur, thirty-four, responded in kind with powerful upward punches as the pace hardly diminished over 12 rounds.
The victor edged the result with judges scorecards of 114-114, narrow lead and 115-112, but both fighters were relentless and full of heart, everything their hero Hatton stood for.
