British light-heavyweight Buatsi earned a win yet unimpressive start to life under recent management with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's activity level likely gained him a split decision in a tight 10-round fight at the Manchester venue.
But Parker found success, landing some telling single shots in a match where the approaches failed to mesh, with excessive holding spoiling the contest.
The officials judged it 96-94 in favor to the winner, with the third a even score.
"It wasn't my greatest display but what defines champions? They win," the victor said in the ringside as he was met by negative reactions from the audience.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts believed the challenger, 31, should have been awarded the decision but the contender experienced the second defeat of his 28-bout career.
The Champion Secures Triumph in Slow Match
Buatsi's progress has stalled in recent times through management issues and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now finds himself trying to realize his potential - maybe in what seems like a last chance - under fresh management.
He started carefully, with the two boxers prepared to take risks in a calculated initial rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after breaking his hand during the bout, was competing in only his second fight at light-heavyweight.
By the halfway stage, the underdog had kept it close, creating difficulties for the favorite, who worked behind a tight guard to narrowly win the more effective rounds.
The crowd's patience diminished during constant clinching, with the challenger slipping to the canvas several times during grappling.
Parker ended stronger, but multiple periods were hard to judge. Nevertheless, previous titleholder Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi advances, but with the caliber of hard hitter Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Motivates Local Rivalry Contest
In the supporting bout, Arthur beat Bradley Rea by split-decision in a outstanding all-Manchester battle to capture the European light-heavyweight belt.
The venue grew hushed for a deeply poignant memorial prior to the bout as ten bells rang in memory of local hero Hatton, who passed away aged 46 in recently.
It was the premier televised match card in the location since the passing of Hatton. As the concluding sound faded, the stillness transitioned to a chant of "there's just one Hatton".
The action during the bout reflected the feeling. The eventual winner was floored by a left hook squarely on the chin in the early round, standing uncertainly to his footing on the referee's count.
But the red-colored equipment of Arthur soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was marked up early, significant bruising appearing under his orbital area as the fighters traded powerful shots.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with powerful upward punches as the pace seldom decreased over the full distance.
The victor narrowly won the result with judges scorecards of draw, narrow lead and 115-112, but both fighters were persistent and brave, all the qualities their idol the legend stood for.
