British light-heavyweight Buatsi made a winning yet unimpressive start to life under recent management with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close 10-round contest at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful single shots in a match where the approaches failed to mesh, with constant grabbing marring the action.
The officials scored it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my best display but what defines champions? They prevail," Buatsi commented in the ring as he was faced negative reactions from the audience.
The British fighter bounced back after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a twentieth professional win.
Various analysts thought Parker, thirty-one, should have been awarded the decision but the British boxer endured the second loss of his 28-fight professional journey.
The Champion Secures Win in Slow Affair
His career development has plateaued in the past few years through promotional disputes and long spells of inactivity.
Previously predicted as the next star of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter willing to be aggressive in a calculated early stages.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who operated with a protective stance to barely take the better periods.
The spectators' acceptance diminished amid constant clinching, with Parker slipping to the canvas various instances during grappling.
Parker finished the stronger, but multiple periods were challenging to assess. However, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Hatton Memorial Inspires Manchester Derby Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by split-decision in a excellent Manchester vs Manchester contest to capture the European light-heavyweight title.
The stadium became quiet for a deeply poignant tribute before the fight as 10 bells rang in memory of the city's native Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the concluding sound faded, the stillness gave way to a chant of "there's only one Ricky Hatton".
The action within the ring reflected the feeling. The eventual winner was knocked down by a significant blow directly to the chin in the initial stage, rising shakily to his footing on the count of eight.
But the red-colored equipment of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was damaged soon, heavy swelling appearing under his face as the fighters exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, responded in kind with stinging uppercuts as the action seldom decreased over the full distance.
Arthur narrowly won the decision with official scores of 114-114, narrow lead and 115-112, but each competitor were persistent and courageous, exactly what their hero the legend embodied.
