British light-heavyweight Buatsi earned a win yet disappointing start to life under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a close 10-round bout 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 constant grabbing disrupting the contest.
The scoring judges scored it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest display but how do champions respond? They succeed," the victor said in the arena as he was met by disapproval from the spectators.
The Londoner bounced back after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts believed the challenger, thirty-one, should have been awarded the decision but the British boxer suffered the second loss of his 28-bout career.
Buatsi Secures Victory in Slow Match
Buatsi's progress has slowed in recent years through contract problems and extended periods of inactivity.
Once tipped as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with both competitors ready to overcommit in a tentative early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after damaging his hand in the contest, was making just his second fight at light heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who operated with a tight guard to barely take the cleaner rounds.
The crowd's patience wore thin amid regular grabbing, with the challenger falling to the floor multiple occasions during grappling.
Parker finished the stronger, but multiple periods were difficult to score. However, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor progresses, but with the likes of power puncher David Benavidez, and Russian star Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Tribute Inspires All-Manchester Contest
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a excellent local rivalry battle to win the continental title.
The arena became quiet for a extremely emotional tribute ahead of the contest as ten bells tolled in remembrance of the city's native Hatton, who passed away 46 years old in September.
It was the first major televised match card in the city since Hatton's death. As the concluding sound disappeared, the silence gave way to a chant of "only one Hatton".
The competition inside the ropes matched the emotion. The eventual winner was floored by a significant blow flush on the chin in the initial stage, rising shakily to his footing on the count of eight.
But the red-colored attire of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was injured early, heavy swelling appearing under his face as the fighters exchanged powerful shots.
Rea, twenty-seven, landed power punches but Arthur, 34, matched the intensity with powerful upward punches as the pace seldom decreased over 12 rounds.
The victor edged the verdict with judges scorecards of 114-114, narrow lead and 115-112, but the two athletes were determined and courageous, everything their hero the legend embodied.
