British light heavyweight Buatsi earned a win yet disappointing start to life under new promoters with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But the challenger landed significant shots, delivering effective clean blows in a match where the techniques never quite clicked, with constant grabbing spoiling the action.
The officials had it 96-94 to the winner, with the remaining official a even score.
"It wasn't my greatest performance but how do champions respond? They win," the victor stated in the arena as he was faced negative reactions from the spectators.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in February - to earn a twentieth professional win.
Various analysts thought Parker, 31, should have been awarded the victory but the British boxer experienced the second loss of his 28-bout career.
Buatsi Claims Triumph in Dull Match
Buatsi's progress has plateaued in recent years through management issues and considerable time of lack of fights.
Previously predicted as the future of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a last chance - under new promotional backing.
He opened tentatively, with both competitors willing to take risks in a tentative opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after damaging his hand in the contest, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for the favorite, who utilized a protective stance to edge the better periods.
The audience's tolerance diminished amid frequent holding, with the challenger going down several times during grappling.
Parker ended stronger, but many rounds were difficult to score. Although, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
The victor moves on, but with the caliber of power puncher Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Tribute Fuels Local Rivalry Contest
In the co-main event, Lyndon Arthur overcame Rea by divided decision in a terrific all-Manchester fight to win the European light heavyweight belt.
The stadium grew hushed for a profoundly moving tribute before the fight as ten bells rang in memory of local hero Hatton, who succumbed 46 years old in recently.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the final chime faded, the quiet gave way to a chant of "only one Ricky Hatton".
The action inside the ropes equaled the feeling. Arthur was floored by a left hook directly to the chin in the initial stage, standing uncertainly to his position on the eight count.
But the Manchester United-red equipment of Arthur soon came forward again. Across the ring, the opponent - in rival City blue - was damaged soon, significant bruising appearing under his orbital area as the duo traded punishing blows.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the action hardly diminished over the full distance.
Arthur narrowly won the verdict with official scores of 114-114, close margin and wider gap, but each competitor were persistent and brave, exactly what their hero the legend represented.
