UK light heavyweight Buatsi earned a win yet underwhelming start to his career under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's work rate likely gained him a majority decision in a tight 10-round contest at the Manchester venue.
But the challenger landed significant shots, connecting with powerful individual punches in a contest where the approaches didn't complement each other, with frequent clinching marring the action.
The officials scored it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my greatest display but what defines champions? They succeed," the victor stated in the ringside as he was faced boos from the audience.
The Londoner got back to winning after his initial pro loss - an thrilling contest with Callum Smith in February - to secure a 20th career victory.
Some ringside observers believed Parker, 31, deserved the win but the Derbyshire fighter endured the second setback of his 28-bout professional journey.
The Champion Secures Triumph in Uneventful Match
Buatsi's progress has stalled in recent times through contract problems and long spells of lack of fights.
Previously predicted as the rising talent of British boxing, he now finds himself trying to achieve expectations - possibly in what seems like a last chance - under recent support.
He started carefully, with neither fighter willing to take risks in a tentative opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second appearance at light heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who utilized a solid defense to narrowly win the cleaner rounds.
The spectators' acceptance wore thin during constant clinching, with Parker going down several times during grappling.
The underdog ended stronger, but many rounds were challenging to assess. However, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Tribute Inspires Local Rivalry Battle
In the co-main event, Lyndon Arthur beat Bradley Rea by split-decision in a outstanding Manchester vs Manchester battle to secure the European light heavyweight title.
The arena fell silent for a deeply poignant tribute ahead of the contest as a bell ceremony sounded in honor of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the concluding sound faded, the stillness became a roar of "there's only one Ricky Hatton".
The action inside the ropes matched the feeling. The eventual winner was knocked down by a left hook squarely on the chin in the second round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red equipment of the fighter soon came forward again. Across the ring, Rea - in competitive blue - was marked up early, heavy swelling forming under his face as the pair traded punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the intensity hardly diminished over 12 rounds.
Arthur barely secured the decision with scoring tallies of draw, 115-113 and 115-112, but the two athletes were persistent and full of heart, all the qualities their hero Hatton stood for.
