UK light-heavyweight Buatsi secured a victory yet disappointing debut to life under fresh promotional backing with a decision win over Zach Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger found success, delivering effective individual punches in a match where the styles didn't complement each other, with excessive holding spoiling the action.
Two judges judged it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest display but what do champions do? They win," the victor said in the arena as he was met by negative reactions from the crowd.
The British fighter got back to winning after his initial pro loss - an epic battle with Callum Smith in February - to secure a 20th career victory.
Several boxing experts believed the challenger, 31, deserved the victory but the Derbyshire fighter endured the second defeat of his 28-fight professional journey.
The Champion Earns Triumph in Dull Match
Buatsi's progress has stalled in recent years through promotional disputes and considerable time of lack of fights.
Once tipped as the next star of UK boxing, he now is positioned trying to achieve expectations - possibly in what seems like a last chance - under fresh management.
He began cautiously, with both competitors prepared to be aggressive in a calculated early stages.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was participating in his second bout at the higher weight class.
By the halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who operated with a tight guard to narrowly win the better rounds.
The audience's tolerance diminished during frequent holding, with Parker slipping to the canvas several times during close exchanges.
Parker closed well, but several stanzas were difficult to score. Nevertheless, ex-champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the caliber of heavy hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Tribute Inspires All-Manchester Battle
In the co-main event, Arthur overcame Rea by divided decision in a outstanding local rivalry fight to capture the European light-heavyweight championship.
The stadium grew hushed for a profoundly moving memorial prior to the bout as ten bells rang in memory of Manchester's own Ricky Hatton, who succumbed aged 46 in recently.
It was the first major televised fight night in the urban center since Hatton's passing. As the final chime ended, the silence became a chant of "there's only one Hatton".
The competition within the ring equaled the feeling. Arthur was sent to the canvas by a left hook squarely on the chin in the initial stage, standing uncertainly to his feet on the referee's count.
But the Manchester United-red equipment of Arthur soon came forward again. From the other corner, the opponent - in competitive blue - was injured soon, significant bruising developing under his face as the pair traded powerful shots.
Rea, 27, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the intensity hardly diminished over the full distance.
The victor barely secured the result with official scores of draw, close margin and wider gap, but both fighters were determined and brave, everything their idol Hatton stood for.
