UK light-heavyweight Buatsi secured a victory yet underwhelming beginning to life under new promoters with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a judges' verdict in a tight 10-round fight at the boxing arena.
But Parker landed significant shots, delivering effective clean blows in a match where the approaches never quite clicked, with excessive holding spoiling the action.
The scoring judges judged it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my best showing but what do champions do? They succeed," Buatsi said in the ring as he was greeted with boos from the crowd.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to secure a 20th career victory.
Various analysts felt the challenger, 31, merited the win but the Derbyshire fighter endured the second setback of his 28-fight career.
The Champion Earns Win in Uneventful Affair
His career development has slowed in recent times through management issues and considerable time of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to realize his potential - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors ready to be aggressive in a cagey early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was participating in his second appearance at light-heavyweight.
By the halfway stage, Parker had made it competitive, making life awkward for Buatsi, who utilized a solid defense to barely take the cleaner periods.
The spectators' acceptance decreased amid regular grabbing, with Parker falling to the floor various instances during grappling.
Parker closed well, but several stanzas were difficult to score. However, former world champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, awarding Buatsi just one round.
The victor advances, but with the likes of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Motivates All-Manchester Contest
In the supporting bout, Lyndon Arthur overcame Rea by divided decision in a excellent Manchester vs Manchester contest to capture the continental belt.
The stadium fell silent for a profoundly moving tribute before the fight as 10 bells tolled in honor of local hero Hatton, who died 46 years old in September.
It was the first major televised fight night in the urban center since the passing of Hatton. As the last bell faded, the quiet gave way to a shout of "there's just one Hatton".
The fighting inside the ropes reflected the sentiment. The eventual winner was floored by a significant blow squarely on the face in the early round, standing uncertainly to his position on the referee's count.
But the red-colored equipment of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was damaged early, noticeable damage forming under his orbital area as the pair landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity hardly diminished over 12 rounds.
The victor edged the verdict with judges scorecards of even score, narrow lead and 115-112, but both fighters were persistent and brave, all the qualities their inspiration Hatton stood for.
