UK light heavyweight Buatsi made a winning yet disappointing debut to his career under fresh promotional backing with a decision win over Zach Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a competitive 10-round fight at the Manchester venue.
But Parker landed significant shots, delivering effective individual punches in a contest where the styles never quite clicked, with excessive holding spoiling the action.
The officials judged it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my finest display but what do champions do? They prevail," Buatsi said in the ring as he was met by boos from the audience.
The British fighter got back to winning after his first professional defeat - an epic battle with Callum Smith in February - to claim a 20th career victory.
Some ringside observers felt the challenger, 31, should have been awarded the decision but the British boxer suffered the second setback of his 28-fight professional journey.
Buatsi Earns Win in Uneventful Encounter
His career development has slowed in recent years through management issues and considerable time of inactivity.
Earlier forecast as the next star of British boxing, he now is positioned trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers willing to take risks in a calculated opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after breaking his hand mid-fight, was making just his second bout at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, causing problems for the favorite, who operated with a tight guard to edge the cleaner stanzas.
The crowd's patience decreased amid frequent holding, with the challenger falling to the floor multiple occasions during grappling.
The underdog closed well, but several stanzas were challenging to assess. Nevertheless, ex-champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Hatton Tribute Motivates All-Manchester Battle
In the co-main event, Lyndon Arthur overcame Rea by split-decision in a outstanding local rivalry fight to secure the European light-heavyweight title.
The arena grew hushed for a profoundly moving homage before the fight as 10 bells tolled in honor of local hero Hatton, who passed away aged 46 in recently.
It was the premier televised match card in the city since Hatton's death. As the last bell ended, the silence transitioned to a roar of "there's just one Hatton".
The competition inside the ropes reflected the sentiment. Arthur was knocked down by a left hook flush on the face in the initial stage, rising shakily to his footing on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was marked up early, noticeable damage appearing under his eye as the fighters traded punishing blows.
The challenger, 27, landed power punches but the champion, 34, responded in kind with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur barely secured the verdict with judges scorecards of even score, close margin and clearer margin, but each competitor were persistent and brave, everything their idol Hatton stood for.
