UK light-heavyweight Buatsi made a winning yet unimpressive start to his career under fresh promotional backing with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a tight ten-round contest at the boxing arena.
But Parker landed significant shots, connecting with powerful individual punches in a fight where the techniques didn't complement each other, with excessive holding disrupting the action.
The officials scored it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my best performance but how do champions respond? They prevail," Buatsi said in the ring as he was greeted with disapproval from the audience.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in February - to claim a 20th pro success.
Some ringside observers thought Parker, 31, merited the win but the British boxer experienced the second setback of his 28-fight career.
The Champion Secures Victory in Slow Encounter
His career development has plateaued in recent years through promotional disputes and considerable time of lack of fights.
Once tipped as the future of British boxing, he now finds himself trying to achieve expectations - possibly in what appears to be a final roll of the dice - under fresh management.
He started carefully, with neither fighter prepared to take risks in a calculated opening few rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand during the bout, was competing in only his second appearance at light heavyweight.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who utilized a tight guard to edge the more effective periods.
The audience's tolerance wore thin because of constant clinching, with Parker going down multiple occasions during close exchanges.
Parker ended stronger, but many rounds were hard to judge. However, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor moves on, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still looks steep.
Hatton Memorial Inspires All-Manchester Battle
In the co-main event, Lyndon Arthur defeated Bradley Rea by split-decision in a outstanding Manchester vs Manchester battle to win the continental title.
The stadium became quiet for a deeply poignant tribute before the fight as 10 bells rang in memory of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the premier televised match card in the urban center since Hatton's death. As the final chime ended, the quiet gave way to a shout of "only one Ricky Hatton".
The fighting during the bout matched the emotion. The eventual winner was floored by a significant blow directly to the jaw in the second round, rising shakily to his feet on the referee's count.
But the Manchester United-red equipment of the fighter soon came forward again. Across the ring, the opponent - in rival City blue - was marked up quickly, heavy swelling developing under his face as the duo exchanged punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with effective uppercuts as the pace seldom decreased over the full distance.
The victor edged the decision with judges scorecards of draw, narrow lead and wider gap, but each competitor were persistent and full of heart, everything their idol the legend embodied.
