UK light heavyweight Buatsi earned a win yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a tight ten-round contest at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a match where the styles didn't complement each other, with frequent clinching spoiling the action.
The officials had it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest display but how do champions respond? They prevail," Buatsi stated in the arena as he was greeted with negative reactions from the audience.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a twentieth professional win.
Several boxing experts believed the challenger, 31, should have been awarded the win but the British boxer suffered the second setback of his 28-bout professional journey.
The Champion Claims Win in Uneventful Match
The fighter's advancement has plateaued in the past few years through promotional disputes and extended periods of lack of fights.
Previously predicted as the next star of UK boxing, he now is positioned trying to realize his potential - possibly in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter willing to be aggressive in a tentative initial rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second fight at the higher weight class.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who utilized a protective stance to barely take the more effective periods.
The crowd's patience wore thin during frequent holding, with the challenger falling to the floor various instances during close exchanges.
The underdog closed well, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Fuels All-Manchester Battle
In the co-main event, Arthur overcame Rea by divided decision in a outstanding local rivalry contest to capture the European light-heavyweight title.
The venue became quiet for a deeply poignant memorial prior to the bout as a bell ceremony sounded in remembrance of local hero Hatton, who passed away aged 46 in recently.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the final chime disappeared, the silence gave way to a chant of "there's only one Hatton".
The fighting within the ring reflected the emotion. Arthur was knocked down by a significant blow flush on the chin in the second round, standing uncertainly to his position on the referee's count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was injured soon, significant bruising appearing under his face as the pair exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with powerful upward punches as the pace seldom decreased over 12 rounds.
Arthur edged the verdict with judges scorecards of even score, close margin and wider gap, but each competitor were determined and brave, everything their inspiration the legend represented.
