British light-heavyweight Buatsi made a winning yet disappointing beginning to his career under fresh promotional backing with a decision win over Zach Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a judges' verdict in a tight 10-round fight at the boxing arena.
But the challenger landed significant shots, connecting with powerful single shots in a contest where the styles failed to mesh, with frequent clinching disrupting the contest.
The officials had it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my best showing but how do champions respond? They win," Buatsi said in the arena as he was met by disapproval from the audience.
The British fighter bounced back after his maiden career setback - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Various analysts thought the challenger, 31, merited the win but the contender endured the second loss of his 28-fight professional journey.
The Champion Claims Win in Dull Encounter
His career development has stalled in the past few years through management issues and considerable time of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to realize his potential - maybe in what seems like a ultimate opportunity - under fresh management.
He started carefully, with both competitors prepared to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in 2022 after suffering a hand injury in the contest, was participating in his second bout at light-heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for Buatsi, who utilized a protective stance to barely take the better periods.
The audience's tolerance wore thin during constant clinching, with Parker falling to the floor several times during close exchanges.
The underdog closed well, but many rounds were hard to judge. Although, previous titleholder the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the presence of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Memorial Inspires Manchester Derby Contest
In the secondary fight, Arthur overcame Rea by divided decision in a excellent local rivalry fight to capture the European light-heavyweight title.
The arena grew hushed for a deeply poignant memorial ahead of the contest as a bell ceremony sounded in remembrance of the city's native Ricky Hatton, who died at age 46 in September.
It was the premier televised boxing event in the location since Hatton's passing. As the concluding sound ended, the silence transitioned to a roar of "there's just one Hatton".
The action during the bout matched the emotion. The eventual winner was floored by a left hook directly to the chin in the initial stage, standing uncertainly to his position on the count of eight.
But the Manchester United-red attire of Arthur soon advanced again. On the opposite side, Rea - in opposing blue - was marked up soon, heavy swelling developing under his eye as the pair landed powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the action seldom decreased over 12 rounds.
The victor edged the decision with judges scorecards of even score, narrow lead and 115-112, but both fighters were persistent and full of heart, exactly what their hero Hatton embodied.
