British light heavyweight Buatsi secured a victory yet unimpressive debut to his career under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a close 10-round fight at the Co-op Live Arena.
But Parker landed significant shots, delivering effective clean blows in a fight where the styles never quite clicked, with frequent clinching spoiling the fight.
Two judges had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They succeed," the victor said in the arena as he was faced disapproval from the audience.
The Londoner got back to winning after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Several boxing experts thought Parker, 31, deserved the decision but the British boxer experienced the second defeat of his 28-match professional journey.
Buatsi Secures Victory in Dull Encounter
The fighter's advancement has slowed in recent years through contract problems and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with neither fighter prepared to overcommit in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after damaging his hand mid-fight, was making just his second bout at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who utilized a protective stance to barely take the more effective stanzas.
The crowd's patience wore thin because of regular grabbing, with the challenger falling to the floor several times during grappling.
The underdog finished the stronger, but many rounds were challenging to assess. Although, previous titleholder Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just one round.
Buatsi moves on, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Tribute Inspires All-Manchester Fight
In the secondary fight, Lyndon Arthur overcame Rea by split-decision in a terrific all-Manchester battle to capture the continental championship.
The stadium grew hushed for a extremely emotional homage ahead of the contest as a bell ceremony rang in remembrance of Manchester's own Ricky Hatton, who died 46 years old in last month.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the concluding sound ended, the quiet transitioned to a roar of "only one Ricky Hatton".
The action within the ring reflected the sentiment. Arthur was knocked down by a left hook flush on the face in the initial stage, standing uncertainly to his footing on the referee's count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was damaged quickly, heavy swelling forming under his orbital area as the pair landed powerful shots.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with effective uppercuts as the pace rarely dropped over 12 rounds.
The victor narrowly won the decision with judges scorecards of even score, close margin and 115-112, but the two athletes were persistent and full of heart, all the qualities their hero the legend embodied.
