British light-heavyweight Buatsi made a winning yet underwhelming start to his career under new promoters with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a tight 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful clean blows in a fight where the approaches failed to mesh, with constant grabbing marring the action.
The officials had it 96-94 for to Buatsi, with the third a even score.
"It wasn't my finest showing but how do champions respond? They win," the victor said in the ring as he was faced negative reactions from the spectators.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to secure a twentieth professional win.
Several boxing experts thought Parker, thirty-one, should have been awarded the win but the contender endured the second setback of his 28-fight professional journey.
The Champion Claims Triumph in Slow Encounter
The fighter's advancement has slowed in the past few years through contract problems and considerable time of inactivity.
Once tipped as the next star of UK boxing, he now finds himself trying to achieve expectations - maybe in what seems like a last chance - under new promotional backing.
He started carefully, with both competitors willing to be aggressive in a cagey initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who operated with a protective stance to barely take the more effective periods.
The audience's tolerance diminished amid constant clinching, with Parker slipping to the canvas multiple occasions during grappling.
The underdog ended stronger, but multiple periods were hard to judge. However, ex-champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Tribute Inspires Manchester Derby Fight
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a outstanding local rivalry contest to capture the European light heavyweight championship.
The stadium became quiet for a deeply poignant memorial before the fight as a bell ceremony tolled in remembrance of Manchester's own Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the concluding sound faded, the silence became a shout of "only one Hatton".
The fighting inside the ropes matched the emotion. Arthur was floored by a left hook directly to the chin in the second round, rising shakily to his position on the referee's count.
But the red-colored shorts of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was damaged quickly, noticeable damage appearing under his face as the duo exchanged powerful shots.
Rea, twenty-seven, landed power punches but the champion, 34, responded in kind with powerful upward punches as the pace hardly diminished over the full distance.
Arthur barely secured the decision with official scores of draw, close margin and wider gap, but both fighters were persistent and brave, everything their hero Hatton embodied.
