UK light-heavyweight Buatsi earned a win yet disappointing beginning to life under recent management with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a competitive 10-round contest at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling individual punches in a match where the approaches failed to mesh, with excessive holding disrupting the action.
The officials judged it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my greatest performance but how do champions respond? They prevail," Buatsi commented in the ringside as he was faced boos from the spectators.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a 20th career victory.
Some ringside observers thought the challenger, thirty-one, deserved the victory but the British boxer experienced the second setback of his 28-bout career.
The Champion Secures Triumph in Slow Encounter
His career development has plateaued in the past few years through contract problems and considerable time of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under recent support.
He started carefully, with neither fighter ready to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was competing in only his second fight at the higher weight class.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who utilized a tight guard to edge the more effective stanzas.
The audience's tolerance decreased during regular grabbing, with Parker going down multiple occasions during grappling.
The underdog closed well, but many rounds were difficult to score. Nevertheless, previous titleholder the boxing analyst - commentating on Dazn - had it strongly leaning for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Inspires All-Manchester Fight
In the supporting bout, Lyndon Arthur beat Rea by divided decision in a excellent all-Manchester contest to secure the European light heavyweight championship.
The venue grew hushed for a profoundly moving memorial before the fight as 10 bells tolled in remembrance of the city's native Ricky Hatton, who passed away at age 46 in September.
It was the initial significant broadcast match card in the urban center since the passing of Hatton. As the concluding sound disappeared, the silence became a chant of "there's just one Hatton".
The competition within the ring reflected the feeling. Arthur was sent to the canvas by a powerful punch flush on the jaw in the second round, getting up unsteadily to his footing on the eight count.
But the traditional red shorts of the fighter soon pressed ahead again. From the other corner, the opponent - in rival City blue - was damaged quickly, heavy swelling developing under his face as the fighters exchanged punishing blows.
The challenger, 27, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity rarely dropped over 12 rounds.
Arthur edged the verdict with official scores of draw, close margin and 115-112, but the two athletes were persistent and courageous, exactly what their idol the legend embodied.
