UK light heavyweight Buatsi made a winning yet underwhelming debut to his career under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a close 10-round fight at the boxing arena.
But Parker found success, connecting with powerful single shots in a fight where the approaches didn't complement each other, with excessive holding marring the contest.
Two judges judged it 96-94 in favor to the winner, with the third a even score.
"It wasn't my finest display but what do champions do? They prevail," Buatsi commented in the ring as he was met by disapproval from the crowd.
The Londoner got back to winning after his initial pro loss - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Various analysts felt Parker, 31, deserved the victory but the contender experienced the second defeat of his 28-match professional journey.
The Champion Secures Triumph in Slow Encounter
His career development has plateaued in recent years through promotional disputes and long spells of inactivity.
Earlier forecast as the next star of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under recent support.
He opened tentatively, with the two boxers willing to be aggressive in a cagey early stages.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the middle rounds, Parker had stayed in contention, causing problems for the favorite, who worked behind a solid defense to narrowly win the better rounds.
The crowd's patience wore thin because of regular grabbing, with Parker going down several times during clinches.
Parker ended stronger, but many rounds were hard to judge. Nevertheless, ex-champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
Buatsi moves on, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Hatton Memorial Motivates Local Rivalry Fight
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a outstanding local rivalry contest to capture the European light-heavyweight belt.
The stadium grew hushed for a extremely emotional tribute ahead of the contest as a bell ceremony tolled in remembrance of the city's native Hatton, who passed away at age 46 in last month.
It was the premier televised match card in the city since Hatton's passing. As the last bell ended, the silence became a roar of "there's just one Hatton".
The action within the ring reflected the sentiment. Arthur was knocked down by a left hook flush on the jaw in the early round, rising shakily to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was damaged soon, heavy swelling appearing under his eye as the pair landed punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the pace hardly diminished over twelve rounds.
The victor edged the decision with judges scorecards of even score, close margin and wider gap, but both fighters were persistent and full of heart, all the qualities their hero Hatton embodied.
