UK light-heavyweight Buatsi secured a victory yet underwhelming beginning to life under recent management with a points victory over Zach Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a close ten-round fight at the Manchester venue.
But Parker found success, delivering effective clean blows in a contest where the styles failed to mesh, with constant grabbing marring the action.
Two judges scored it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my greatest showing but what do champions do? They succeed," Buatsi said in the ring as he was met by negative reactions from the crowd.
The Londoner bounced back after his maiden career setback - an epic battle with Callum Smith in February - to secure a 20th career victory.
Several boxing experts thought the challenger, 31, should have been awarded the victory but the Derbyshire fighter suffered the second defeat of his 28-bout professional journey.
Buatsi Earns Win in Dull Encounter
The fighter's advancement has slowed in recent years through contract problems and considerable time of inactivity.
Once tipped as the future of the British fight scene, he now is positioned trying to achieve expectations - possibly in what feels like a last chance - under new promotional backing.
He opened tentatively, with the two boxers willing to overcommit in a calculated early stages.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, making life awkward for Buatsi, who utilized a protective stance to barely take the more effective periods.
The audience's tolerance diminished during frequent holding, with the challenger slipping to the canvas multiple occasions during close exchanges.
Parker ended stronger, but several stanzas were challenging to assess. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the presence of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Tribute Inspires Manchester Derby Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding all-Manchester contest to capture the continental belt.
The arena became quiet for a profoundly moving memorial before the fight as 10 bells sounded in honor of the city's native Hatton, who died aged 46 in last month.
It was the first major televised boxing event in the location since Hatton's death. As the concluding sound faded, the quiet became a shout of "there's only one Hatton".
The competition inside the ropes reflected the feeling. Arthur was floored by a powerful punch directly to the chin in the second round, rising shakily to his position on the eight count.
But the red-colored equipment of the fighter soon came forward again. On the opposite side, the opponent - in competitive blue - was marked up soon, significant bruising developing under his eye as the duo exchanged powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the intensity hardly diminished over the full distance.
The victor edged the verdict with judges scorecards of even score, narrow lead and clearer margin, but the two athletes were determined and brave, all the qualities their idol the legend represented.
