British light heavyweight Buatsi earned a win yet unimpressive debut to his career under fresh promotional backing with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a majority decision in a tight 10-round bout at the Manchester venue.
But Parker found success, delivering effective individual punches in a fight where the styles failed to mesh, with frequent clinching disrupting the contest.
Two judges judged it 96-94 to the winner, with the final judge a even score.
"It wasn't my finest showing but what defines champions? They succeed," the victor commented in the ring as he was met by boos from the spectators.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Various analysts believed Parker, 31, merited the victory but the Derbyshire fighter suffered the second loss of his 28-fight professional journey.
The Champion Earns Triumph in Uneventful Encounter
Buatsi's progress has slowed in recent years through promotional disputes and long spells of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to realize his potential - maybe in what seems like a final roll of the dice - under fresh management.
He began cautiously, with the two boxers willing to be aggressive in a calculated early stages.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after damaging his hand during the bout, was making just his second bout at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for the favorite, who operated with a solid defense to edge the more effective periods.
The crowd's patience diminished because of constant clinching, with the challenger falling to the floor multiple occasions during clinches.
Parker closed well, but several stanzas were difficult to score. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Hatton Tribute Inspires All-Manchester Battle
In the supporting bout, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding Manchester vs Manchester battle to win the European light-heavyweight belt.
The stadium grew hushed for a profoundly moving homage before the fight as a bell ceremony sounded in remembrance of the city's native Ricky Hatton, who succumbed 46 years old in last month.
It was the premier televised boxing event in the location since Hatton's passing. As the final chime ended, the stillness became a chant of "there's only one Hatton".
The action inside the ropes matched the sentiment. Arthur was knocked down by a significant blow directly to the chin in the initial stage, standing uncertainly to his position on the referee's count.
But the Manchester United-red equipment of the fighter soon advanced again. On the opposite side, the opponent - in opposing blue - was damaged early, heavy swelling developing under his face as the pair landed punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over 12 rounds.
Arthur edged the result with scoring tallies of even score, narrow lead and clearer margin, but each competitor were persistent and brave, all the qualities their idol the legend embodied.
