British light-heavyweight Buatsi earned a win yet disappointing beginning to life under fresh promotional backing with a decision win over Zach Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive 10-round fight at the Co-op Live Arena.
But Parker landed significant shots, landing some telling individual punches in a contest where the approaches never quite clicked, with frequent clinching disrupting the action.
The scoring judges judged it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my finest display but what defines champions? They win," Buatsi stated in the ringside as he was faced boos from the crowd.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in February - to claim a 20th career victory.
Various analysts thought Parker, thirty-one, should have been awarded the decision but the British boxer endured the second defeat of his 28-fight professional journey.
The Champion Claims Victory in Uneventful Encounter
His career development has slowed in recent years through contract problems and extended periods of lack of fights.
Previously predicted as the future of British boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with the two boxers prepared to be aggressive in a calculated initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after suffering a hand injury in the contest, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who operated with a solid defense to barely take the cleaner stanzas.
The spectators' acceptance diminished during regular grabbing, with the challenger going down multiple occasions during clinches.
The underdog finished the stronger, but several stanzas were challenging to assess. However, ex-champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the caliber of heavy hitter Benavidez, and Russian star Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Inspires All-Manchester Battle
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a outstanding local rivalry battle to win the European light-heavyweight championship.
The arena fell silent for a deeply poignant tribute prior to the bout as ten bells sounded in honor of the city's native Ricky Hatton, who died aged 46 in September.
It was the first major televised match card in the location since the passing of Hatton. As the concluding sound disappeared, the stillness became a roar of "there's only one Ricky Hatton".
The competition within the ring equaled the feeling. Arthur was sent to the canvas by a significant blow squarely on the face in the second round, standing uncertainly to his footing on the count of eight.
But the traditional red equipment of the fighter soon came forward again. Across the ring, the opponent - in competitive blue - was marked up soon, heavy swelling developing under his eye as the pair landed punishing blows.
Rea, 27, connected with strong blows but the champion, thirty-four, responded in kind with effective uppercuts as the intensity rarely dropped over 12 rounds.
Arthur edged the result with judges scorecards of draw, narrow lead and 115-112, but each competitor were persistent and full of heart, exactly what their inspiration the legend represented.
