UK light-heavyweight Buatsi made a winning yet unimpressive beginning to his career under new promoters with a decision win over Zach Parker in Manchester.
The Olympic medal winner's work rate likely gained him a split decision in a tight 10-round bout at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a contest where the styles never quite clicked, with constant grabbing spoiling the fight.
The officials scored it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my best showing but how do champions respond? They succeed," the victor commented in the ringside as he was met by disapproval from the spectators.
The Londoner bounced back after his initial pro loss - an epic battle with Callum Smith in last winter - to secure a 20th career victory.
Some ringside observers believed Parker, thirty-one, merited the decision but the Derbyshire fighter suffered the second setback of his 28-bout professional journey.
Buatsi Earns Triumph in Dull Affair
Buatsi's progress has stalled in the past few years through promotional disputes and extended periods of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to realize his potential - perhaps in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with the two boxers prepared to take risks in a calculated initial rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was making just his second bout at the higher weight class.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who operated with a solid defense to barely take the better periods.
The spectators' acceptance diminished because of constant clinching, with the challenger going down several times during grappling.
Parker ended stronger, but several stanzas were challenging to assess. Although, ex-champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just one round.
The victor moves on, but with the presence of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Tribute Motivates Manchester Derby Fight
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a excellent Manchester vs Manchester battle to capture the European light-heavyweight championship.
The stadium grew hushed for a extremely emotional tribute prior to the bout as 10 bells rang in memory of the city's native Ricky Hatton, who succumbed at age 46 in recently.
It was the first major televised fight night in the city since Hatton's passing. As the final chime faded, the silence transitioned to a chant of "only one Hatton".
The competition during the bout reflected the sentiment. Arthur was sent to the canvas by a left hook squarely on the jaw in the initial stage, standing uncertainly to his position on the eight count.
But the Manchester United-red equipment of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was injured soon, significant bruising forming under his eye as the pair exchanged punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with effective uppercuts as the intensity hardly diminished over 12 rounds.
Arthur narrowly won the decision with judges scorecards of draw, 115-113 and wider gap, but the two athletes were determined and courageous, everything their idol the legend represented.
