UK light heavyweight Buatsi secured a victory yet disappointing start to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a close 10-round bout at the boxing arena.
But the challenger landed significant shots, landing some telling single shots in a fight where the styles failed to mesh, with excessive holding disrupting the fight.
The scoring judges judged it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest performance but what defines champions? They win," Buatsi commented in the ringside as he was met by disapproval from the spectators.
The Londoner returned to winning ways after his first professional defeat - an epic battle with Callum Smith in last winter - to claim a 20th career victory.
Various analysts felt Parker, thirty-one, merited the decision but the Derbyshire fighter suffered the second setback of his 28-fight career.
The Champion Secures Win in Dull Affair
The fighter's advancement has plateaued in recent times through promotional disputes and long spells of inactivity.
Once tipped as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under recent support.
He started carefully, with neither fighter prepared to take risks in a tentative initial rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second bout at light heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who operated with a tight guard to edge the cleaner rounds.
The spectators' acceptance decreased because of regular grabbing, with Parker going down various instances during clinches.
The underdog closed well, but multiple periods were difficult to score. Nevertheless, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi advances, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - on this evidence - still seems difficult.
Hatton Homage Fuels All-Manchester Battle
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a terrific all-Manchester contest to capture the European light heavyweight title.
The arena grew hushed for a profoundly moving tribute ahead of the contest as 10 bells tolled in remembrance of Manchester's own Ricky Hatton, who passed away 46 years old in last month.
It was the first major televised boxing event in the city since Hatton's death. As the concluding sound disappeared, the silence transitioned to a roar of "only one Hatton".
The competition within the ring matched the feeling. Arthur was floored by a left hook squarely on the jaw in the second round, standing uncertainly to his feet on the referee's count.
But the red-colored attire of the fighter soon pressed ahead again. Across the ring, the opponent - in competitive blue - was injured quickly, noticeable damage appearing under his eye as the duo traded powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the intensity rarely dropped over twelve rounds.
Arthur narrowly won the result with official scores of 114-114, close margin and clearer margin, but both fighters were relentless and courageous, everything their idol Hatton stood for.
