British light-heavyweight Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive 10-round contest at the Co-op Live Arena.
But the challenger found success, connecting with powerful clean blows in a match where the styles didn't complement each other, with excessive holding marring the action.
The officials had it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best showing but what defines champions? They win," the victor commented in the ringside as he was faced boos from the audience.
The Londoner bounced back after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts thought Parker, thirty-one, deserved the decision but the Derbyshire fighter suffered the second defeat of his 28-fight professional journey.
The Champion Secures Win in Uneventful Affair
The fighter's advancement has stalled in recent times through management issues and long spells of inactivity.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to realize his potential - maybe in what feels like a last chance - under new promotional backing.
He began cautiously, with neither fighter prepared to take risks in a calculated early stages.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second bout at the higher weight class.
By the fight's midpoint, the underdog had kept it close, creating difficulties for Buatsi, who worked behind a tight guard to edge the cleaner rounds.
The audience's tolerance diminished because of frequent holding, with Parker slipping to the canvas multiple occasions during grappling.
Parker ended stronger, but multiple periods were challenging to assess. However, ex-champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, awarding Buatsi just one round.
Buatsi progresses, but with the caliber of hard hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Hatton Tribute Fuels Manchester Derby Contest
In the secondary fight, Arthur defeated Rea by close verdict in a terrific all-Manchester contest to capture the European light heavyweight championship.
The stadium became quiet for a deeply poignant memorial before the fight as 10 bells tolled in remembrance of local hero Hatton, who died at age 46 in recently.
It was the first major televised fight night in the urban center since Hatton's death. As the concluding sound faded, the stillness became a chant of "only one Ricky Hatton".
The action within the ring reflected the feeling. The eventual winner was floored by a significant blow flush on the jaw in the second round, rising shakily to his position on the count of eight.
But the traditional red equipment of Arthur soon advanced again. From the other corner, the opponent - in opposing blue - was damaged quickly, significant bruising developing under his orbital area as the pair traded powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity rarely dropped over twelve rounds.
The victor barely secured the verdict with judges scorecards of draw, close margin and clearer margin, but each competitor were relentless and brave, all the qualities their idol the legend represented.
