UK light-heavyweight Buatsi made a winning yet underwhelming start to his career under fresh promotional backing with a decision win over Zach Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a tight 10-round contest at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a fight where the techniques never quite clicked, with constant grabbing disrupting the fight.
The scoring judges had it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my finest performance but what defines champions? They succeed," the victor said in the ringside as he was faced disapproval from the crowd.
The Londoner bounced back after his maiden career setback - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Several boxing experts believed Parker, 31, should have been awarded the decision but the Derbyshire fighter endured the second defeat of his 28-match professional journey.
Buatsi Earns Win in Slow Affair
His career development has slowed in the past few years through management issues and extended periods of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to fulfil that early promise - possibly in what feels like a last chance - under recent support.
He started carefully, with neither fighter willing to overcommit in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after damaging his hand during the bout, was making just his second appearance at the higher weight class.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a solid defense to barely take the better rounds.
The audience's tolerance diminished because of frequent holding, with the challenger slipping to the canvas several times during clinches.
The underdog closed well, but multiple periods were difficult to score. Although, previous titleholder Carl Frampton - commentating on Dazn - had it particularly wide for Parker, giving Buatsi just only one stanza.
The victor moves on, but with the presence of hard hitter Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Homage Inspires All-Manchester Battle
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a excellent Manchester vs Manchester fight to secure the European light heavyweight belt.
The stadium fell silent for a extremely emotional memorial before the fight as a bell ceremony rang in remembrance of the city's native Ricky Hatton, who passed away at age 46 in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the concluding sound ended, the stillness gave way to a shout of "only one Hatton".
The action inside the ropes reflected the feeling. The eventual winner was floored by a left hook squarely on the chin in the initial stage, rising shakily to his position on the referee's count.
But the traditional red shorts of Arthur soon came forward again. On the opposite side, the opponent - in opposing blue - was injured early, heavy swelling forming under his orbital area as the fighters exchanged hard punches.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the action seldom decreased over the full distance.
The victor edged the decision with judges scorecards of draw, narrow lead and clearer margin, but the two athletes were determined and brave, exactly what their idol Hatton represented.
