UK light heavyweight Buatsi earned a win yet unimpressive debut to his career under recent management 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 contest at the Manchester venue.
But Parker had his moments, delivering effective individual punches in a contest where the approaches failed to mesh, with constant grabbing disrupting the fight.
The officials scored it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my finest showing but what defines champions? They win," Buatsi stated in the ring as he was faced boos from the crowd.
The Londoner bounced back after his maiden career setback - an epic battle with Callum Smith in February - to claim a 20th career victory.
Some ringside observers felt the challenger, 31, should have been awarded the victory but the British boxer experienced the second defeat of his 28-match professional journey.
The Champion Secures Win in Uneventful Match
Buatsi's progress has plateaued in recent times through contract problems and long spells of lack of fights.
Once tipped as the future of British boxing, he now is positioned trying to realize his potential - maybe in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers ready to take risks in a tentative opening few rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand during the bout, was making just his second bout at the higher weight class.
By the fight's midpoint, the underdog had kept it close, causing problems for the favorite, who utilized a tight guard to narrowly win the cleaner stanzas.
The spectators' acceptance wore thin because of frequent holding, with Parker slipping to the canvas various instances during close exchanges.
Parker ended stronger, but several stanzas were difficult to score. Although, previous titleholder the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
The victor advances, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Ricky Hatton Homage Motivates Local Rivalry Contest
In the supporting bout, Lyndon Arthur overcame Rea by close verdict in a excellent Manchester vs Manchester contest to win the European light-heavyweight championship.
The stadium grew hushed for a profoundly moving memorial before the fight as a bell ceremony sounded in memory of the city's native Ricky Hatton, who died aged 46 in last month.
It was the premier televised boxing event in the location since Hatton's death. As the concluding sound disappeared, the quiet transitioned to a chant of "there's only one Hatton".
The competition inside the ropes equaled the emotion. Arthur was sent to the canvas by a left hook directly to the face in the second round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. Across the ring, the opponent - in competitive blue - was marked up soon, heavy swelling appearing under his face as the pair landed punishing blows.
The challenger, 27, delivered effective strikes but Arthur, 34, fought fire with fire with effective uppercuts as the action seldom decreased over the full distance.
Arthur edged the decision with official scores of 114-114, close margin and 115-112, but the two athletes were relentless and full of heart, exactly what their idol the legend stood for.
