UK light heavyweight Buatsi earned a win yet disappointing debut to his career under new promoters with a decision win over Zach Parker in Manchester.
The Olympic medal winner's work rate likely gained him a judges' verdict in a tight 10-round bout at the Manchester venue.
But Parker had his moments, connecting with powerful clean blows in a match where the styles never quite clicked, with constant grabbing marring the fight.
The scoring judges scored it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my finest showing but what do champions do? They succeed," the victor stated in the ringside as he was met by negative reactions from the audience.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a 20th pro success.
Some ringside observers thought Parker, 31, deserved the decision but the contender suffered the second defeat of his 28-bout professional journey.
The Champion Claims Win in Slow Affair
His career development has plateaued in recent years through management issues and long spells of lack of fights.
Previously predicted as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter prepared to be aggressive in a tentative early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in 2022 after breaking his hand during the bout, was making just his second bout at the higher weight class.
By the middle rounds, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a tight guard to edge the more effective periods.
The spectators' acceptance diminished amid constant clinching, with the challenger falling to the floor several times during clinches.
Parker closed well, but multiple periods were hard to judge. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Hatton Tribute Fuels Local Rivalry Battle
In the secondary fight, Lyndon Arthur defeated Bradley Rea by split-decision in a terrific local rivalry battle to capture the European light heavyweight championship.
The venue grew hushed for a deeply poignant homage ahead of the contest as 10 bells sounded in memory of Manchester's own Hatton, who passed away aged 46 in last month.
It was the premier televised match card in the location since Hatton's death. As the concluding sound faded, the silence transitioned to a roar of "there's only one Hatton".
The fighting within the ring equaled the emotion. The eventual winner was knocked down by a significant blow squarely on the jaw in the second round, standing uncertainly to his feet on the count of eight.
But the Manchester United-red attire of Arthur soon advanced again. Across the ring, Rea - in rival City blue - was damaged early, noticeable damage forming under his face as the duo traded hard punches.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over 12 rounds.
The victor barely secured the result with judges scorecards of 114-114, narrow lead and clearer margin, but each competitor were relentless and full of heart, exactly what their hero Hatton stood for.
