British light-heavyweight Buatsi earned a win yet unimpressive beginning to life under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a tight 10-round contest at the boxing arena.
But Parker found success, delivering effective individual punches in a contest where the approaches failed to mesh, with excessive holding disrupting the action.
Two judges judged it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my greatest display but how do champions respond? They win," Buatsi commented in the ring as he was faced negative reactions from the spectators.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers believed Parker, 31, deserved the win but the British boxer suffered the second loss of his 28-match professional journey.
The Champion Earns Win in Slow Match
The fighter's advancement has slowed in recent years through contract problems and long spells of inactivity.
Once tipped as the next star of British boxing, he now stands trying to achieve expectations - possibly in what feels like a last chance - under recent support.
He started carefully, with neither fighter prepared to be aggressive in a calculated opening few rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in 2022 after suffering a hand injury in the contest, was making just his second fight at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for Buatsi, who utilized a tight guard to narrowly win the better stanzas.
The spectators' acceptance decreased because of regular grabbing, with the challenger falling to the floor various instances during clinches.
Parker ended stronger, but many rounds were difficult to score. Nevertheless, former world champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just a single round.
The victor advances, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Memorial Inspires Local Rivalry Contest
In the secondary fight, Arthur overcame Bradley Rea by divided decision in a outstanding all-Manchester fight to secure the European light-heavyweight championship.
The stadium grew hushed for a deeply poignant homage prior to the bout as ten bells sounded in remembrance of the city's native Hatton, who died at age 46 in recently.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the concluding sound disappeared, the stillness transitioned to a shout of "there's just one Ricky Hatton".
The fighting inside the ropes matched the emotion. The eventual winner was sent to the canvas by a powerful punch directly to the chin in the initial stage, rising shakily to his feet on the referee's count.
But the red-colored equipment of Arthur soon came forward again. On the opposite side, the opponent - in opposing blue - was injured early, heavy swelling forming under his face as the duo traded powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the action rarely dropped over the full distance.
Arthur narrowly won the decision with official scores of 114-114, 115-113 and clearer margin, but the two athletes were relentless and brave, all the qualities their inspiration Hatton stood for.
