UK light heavyweight Buatsi earned a win yet unimpressive debut to life under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a tight 10-round contest at the boxing arena.
But the challenger landed significant shots, connecting with powerful clean blows in a match where the techniques didn't complement each other, with excessive holding disrupting the contest.
The officials judged it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my finest performance but what do champions do? They succeed," Buatsi commented in the ringside as he was faced disapproval from the crowd.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts felt Parker, 31, deserved the decision but the British boxer endured the second setback of his 28-match professional journey.
The Champion Claims Win in Slow Match
The fighter's advancement has slowed in the past few years through management issues and considerable time of inactivity.
Earlier forecast as the next star of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under fresh management.
He started carefully, with neither fighter ready to overcommit in a tentative opening few rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after suffering a hand injury 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, making life awkward for Buatsi, who utilized a solid defense to barely take the better periods.
The audience's tolerance diminished during constant clinching, with Parker slipping to the canvas several times during grappling.
The underdog closed well, but multiple periods were challenging to assess. Although, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just only one stanza.
The victor moves on, but with the likes of power puncher Benavidez, and Russian star Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Hatton Homage Inspires Local Rivalry Fight
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a terrific all-Manchester contest to capture the continental title.
The arena fell silent for a extremely emotional memorial ahead of the contest as 10 bells rang in honor of Manchester's own Ricky Hatton, who died 46 years old in last month.
It was the first major televised match card in the city since Hatton's death. As the concluding sound faded, the quiet gave way to a chant of "there's only one Hatton".
The fighting inside the ropes matched the emotion. The eventual winner was knocked down by a significant blow directly to the face in the second round, standing uncertainly to his feet on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was marked up early, significant bruising forming under his face as the fighters exchanged punishing blows.
The challenger, 27, delivered effective strikes but the champion, 34, matched the intensity with effective uppercuts as the pace rarely dropped over twelve rounds.
Arthur edged the decision with judges scorecards of draw, close margin and wider gap, but each competitor were relentless and brave, all the qualities their hero Hatton represented.
