UK light heavyweight Buatsi earned a win yet disappointing start to life under new promoters with a points victory over Zach Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a majority decision in a close ten-round bout at the Manchester venue.
But Parker found success, landing some telling clean blows in a fight where the techniques failed to mesh, with excessive holding disrupting the contest.
Two judges had it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my best performance but what defines champions? They succeed," the victor commented in the ring as he was faced boos from the crowd.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to secure a twentieth professional win.
Several boxing experts thought the challenger, 31, deserved the win but the contender suffered the second loss of his 28-match professional journey.
Buatsi Claims Win in Slow Match
His career development has stalled in the past few years through promotional disputes and considerable time of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a last chance - under recent support.
He began cautiously, with both competitors willing to be aggressive in a calculated early stages.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who utilized a protective stance to narrowly win the more effective periods.
The crowd's patience diminished because of constant clinching, with the challenger falling to the floor multiple occasions during close exchanges.
Parker ended stronger, but many rounds were challenging to assess. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, giving Buatsi just a single round.
The victor advances, but with the likes of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Motivates All-Manchester Fight
In the supporting bout, Arthur defeated Rea by divided decision in a terrific Manchester vs Manchester contest to secure the European light-heavyweight belt.
The stadium became quiet for a profoundly moving tribute ahead of the contest as a bell ceremony sounded in remembrance of Manchester's own Ricky Hatton, who succumbed 46 years old in recently.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the final chime faded, the silence became a shout of "only one Ricky Hatton".
The action inside the ropes reflected the emotion. Arthur was floored by a powerful punch squarely on the chin in the second round, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red attire of the fighter soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was injured quickly, noticeable damage developing under his orbital area as the duo traded punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor edged the result with judges scorecards of 114-114, close margin and wider gap, but the two athletes were determined and full of heart, all the qualities their inspiration Hatton embodied.
