UK light heavyweight Buatsi earned a win yet disappointing debut to life under recent management with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a majority decision in a tight 10-round fight at the Co-op Live Arena.
But Parker had his moments, delivering effective clean blows in a contest where the techniques never quite clicked, with frequent clinching disrupting the contest.
Two judges had it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my best performance but what defines champions? They prevail," Buatsi said in the ring as he was faced disapproval from the crowd.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers felt Parker, 31, should have been awarded the victory but the Derbyshire fighter endured the second defeat of his 28-bout career.
Buatsi Earns Triumph in Dull Encounter
The fighter's advancement has stalled in recent times through promotional disputes and considerable time of lack of fights.
Once tipped as the rising talent of UK boxing, he now finds himself trying to realize his potential - possibly in what seems like a last chance - under new promotional backing.
He began cautiously, with the two boxers willing to overcommit in a cagey initial rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was participating in his second bout at light-heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for the favorite, who utilized a protective stance to barely take the more effective rounds.
The spectators' acceptance wore thin because of regular grabbing, with the challenger falling to the floor several times during close exchanges.
The underdog finished the stronger, but many rounds were challenging to assess. Nevertheless, previous titleholder Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Homage Inspires All-Manchester Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific local rivalry battle to capture the European light-heavyweight title.
The stadium fell silent for a extremely emotional tribute prior to the bout as ten bells tolled in honor of local hero Ricky Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast match card in the urban center since the passing of Hatton. As the concluding sound faded, the stillness became a roar of "there's only one Ricky Hatton".
The fighting inside the ropes reflected the feeling. Arthur was knocked down by a powerful punch directly to the face in the early round, getting up unsteadily to his feet on the referee's count.
But the red-colored shorts of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was marked up soon, heavy swelling developing under his face as the pair exchanged punishing blows.
Rea, 27, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor barely secured the verdict with judges scorecards of even score, narrow lead and 115-112, but each competitor were determined and courageous, everything their hero Hatton stood for.
