UK light heavyweight Buatsi earned a win yet disappointing beginning to his career under recent management with a decision win over Zach Parker in Manchester.
The Olympic medal winner's work rate likely gained him a judges' verdict in a tight 10-round fight at the Co-op Live Arena.
But Parker found success, connecting with powerful clean blows in a fight where the approaches never quite clicked, with frequent clinching spoiling the action.
Two judges judged it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my finest showing but what defines champions? They win," the victor said in the ringside as he was faced disapproval from the audience.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Several boxing experts believed Parker, 31, should have been awarded the victory but the Derbyshire fighter suffered the second setback of his 28-match career.
Buatsi Earns Win in Uneventful Encounter
The fighter's advancement has plateaued in the past few years through contract problems and extended periods of inactivity.
Once tipped as the next star of British boxing, he now stands trying to achieve expectations - perhaps in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter ready to overcommit in a tentative initial rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was making just his second fight at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to barely take the cleaner rounds.
The audience's tolerance decreased because of constant clinching, with the challenger falling to the floor several times during grappling.
Parker finished the stronger, but multiple periods were challenging to assess. Nevertheless, ex-champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, awarding Buatsi just one round.
The victor moves on, but with the presence of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Hatton Memorial Motivates Local Rivalry Fight
In the supporting bout, Lyndon Arthur beat Rea by close verdict in a terrific local rivalry fight to capture the European light heavyweight championship.
The venue grew hushed for a deeply poignant memorial ahead of the contest as a bell ceremony rang in honor of local hero Hatton, who died 46 years old in September.
It was the first major televised match card in the urban center since Hatton's passing. As the concluding sound ended, the stillness gave way to a shout of "there's only one Hatton".
The action during the bout equaled the emotion. Arthur was sent to the canvas by a powerful punch flush on the face in the second round, standing uncertainly to his footing on the referee's count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. On the opposite side, Rea - in opposing blue - was marked up soon, significant bruising forming under his face as the duo exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with effective uppercuts as the pace seldom decreased over 12 rounds.
Arthur narrowly won the verdict with scoring tallies of draw, narrow lead and 115-112, but each competitor were relentless and brave, all the qualities their inspiration Hatton embodied.
