British light-heavyweight Buatsi made a winning yet disappointing start to his career under fresh promotional backing with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a close 10-round contest at the boxing arena.
But Parker had his moments, landing some telling single shots in a fight where the techniques failed to mesh, with constant grabbing marring the contest.
Two judges had it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best display but how do champions respond? They prevail," the victor said in the ringside as he was greeted with negative reactions from the crowd.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts felt the challenger, thirty-one, merited the decision but the contender suffered the second defeat of his 28-bout professional journey.
Buatsi Earns Triumph in Slow Match
The fighter's advancement has plateaued in the past few years through promotional disputes and considerable time of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to realize his potential - perhaps in what feels like a last chance - under new promotional backing.
He opened tentatively, with both competitors willing to take risks in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after breaking his hand in the contest, was competing in only his second appearance at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a solid defense to edge the cleaner rounds.
The crowd's patience decreased because of constant clinching, with the challenger slipping to the canvas various instances during grappling.
Parker closed well, but multiple periods were difficult to score. However, previous titleholder Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor advances, but with the caliber of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Hatton Memorial Fuels Manchester Derby Fight
In the secondary fight, Arthur beat Bradley Rea by split-decision in a outstanding all-Manchester battle to capture the continental championship.
The stadium fell silent for a deeply poignant tribute before the fight as ten bells rang in honor of the city's native Ricky Hatton, who succumbed at age 46 in recently.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the concluding sound disappeared, the stillness transitioned to a shout of "there's just one Hatton".
The competition within the ring matched the feeling. Arthur was floored by a left hook directly to the face in the second round, standing uncertainly to his position on the count of eight.
But the traditional red equipment of Arthur soon pressed ahead again. Across the ring, Rea - in competitive blue - was damaged quickly, significant bruising appearing under his orbital area as the duo traded punishing blows.
Rea, 27, delivered effective strikes but the champion, thirty-four, responded in kind with effective uppercuts as the pace seldom decreased over 12 rounds.
Arthur barely secured the result with official scores of even score, narrow lead and 115-112, but both fighters were persistent and full of heart, everything their idol the legend stood for.
