British light heavyweight Buatsi secured a victory yet disappointing debut to life under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a close ten-round fight at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a contest where the approaches never quite clicked, with constant grabbing disrupting the action.
The officials judged it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best display but what do champions do? They win," the victor said in the arena as he was greeted with disapproval from the audience.
The Londoner bounced back after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a 20th pro success.
Various analysts felt the challenger, thirty-one, deserved the win but the contender suffered the second defeat of his 28-bout professional journey.
The Champion Secures Triumph in Uneventful Affair
Buatsi's progress has stalled in recent times through contract problems and long spells of inactivity.
Previously predicted as the future of UK boxing, he now is positioned trying to achieve expectations - possibly in what feels like a last chance - under new promotional backing.
He began cautiously, with both competitors ready to be aggressive in a tentative opening few rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after damaging his hand during the bout, was participating in his second appearance at the higher weight class.
By the halfway stage, the underdog had stayed in contention, causing problems for Buatsi, who operated with a protective stance to narrowly win the better rounds.
The crowd's patience decreased amid constant clinching, with the challenger going down several times during grappling.
Parker ended stronger, but multiple periods were challenging to assess. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
The victor advances, but with the likes of power puncher Benavidez, and Russian champion Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Tribute Motivates All-Manchester Battle
In the supporting bout, Lyndon Arthur overcame Rea by close verdict in a excellent local rivalry battle to secure the European light-heavyweight championship.
The arena grew hushed for a deeply poignant tribute ahead of the contest as a bell ceremony sounded in memory of Manchester's own Ricky Hatton, who died 46 years old in last month.
It was the premier televised match card in the urban center since the passing of Hatton. As the concluding sound disappeared, the quiet gave way to a roar of "there's just one Ricky Hatton".
The competition inside the ropes reflected the sentiment. Arthur was knocked down by a powerful punch flush on the jaw in the initial stage, rising shakily to his position on the eight count.
But the traditional red attire of Arthur soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was injured quickly, significant bruising forming under his face as the duo traded powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the pace hardly diminished over twelve rounds.
Arthur barely secured the result with judges scorecards of 114-114, narrow lead and wider gap, but each competitor were relentless and courageous, all the qualities their hero the legend stood for.
