British light heavyweight Buatsi earned a win yet disappointing debut to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic medal winner's punch output likely gained him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But Parker landed significant shots, landing some telling individual punches in a match where the approaches didn't complement each other, with constant grabbing marring the contest.
The officials had it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my greatest showing but how do champions respond? They succeed," the victor said in the ringside as he was met by disapproval from the spectators.
The British fighter bounced back after his initial pro loss - an epic battle with Callum Smith in February - to secure a 20th career victory.
Various analysts believed the challenger, thirty-one, deserved the victory but the Derbyshire fighter suffered the second setback of his 28-match career.
The Champion Earns Victory in Slow Match
Buatsi's progress has stalled in the past few years through contract problems and long spells of inactivity.
Earlier forecast as the future of British boxing, he now stands trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under recent support.
He started carefully, with neither fighter prepared to overcommit in a cagey initial rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was participating in his second fight at the higher weight class.
By the middle rounds, the underdog had stayed in contention, making life awkward for the favorite, who operated with a tight guard to edge the more effective rounds.
The spectators' acceptance wore thin because of constant clinching, with Parker slipping to the canvas multiple occasions during close exchanges.
The underdog finished the stronger, but several stanzas were challenging to assess. However, previous titleholder Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Hatton Homage Inspires Local Rivalry Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding all-Manchester fight to capture the European light heavyweight championship.
The stadium became quiet for a profoundly moving homage prior to the bout as a bell ceremony rang in memory of Manchester's own Ricky Hatton, who died 46 years old in last month.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the concluding sound faded, the silence transitioned to a shout of "there's only one Hatton".
The competition inside the ropes reflected the sentiment. Arthur was floored by a significant blow flush on the jaw in the second round, getting up unsteadily to his feet on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was damaged quickly, significant bruising developing under his face as the duo landed powerful shots.
The challenger, 27, connected with strong blows but Arthur, thirty-four, responded in kind with effective uppercuts as the intensity seldom decreased over twelve rounds.
Arthur barely secured the result with scoring tallies of draw, 115-113 and clearer margin, but the two athletes were persistent and courageous, everything their idol the legend stood for.
