UK light heavyweight Buatsi made a winning yet disappointing start to his career under recent management with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a competitive 10-round bout at the Co-op Live Arena.
But Parker had his moments, delivering effective clean blows in a fight where the techniques never quite clicked, with constant grabbing marring the fight.
The scoring judges scored it 96-94 to Buatsi, with the final judge a 95-95.
"It wasn't my best display but what defines champions? They prevail," the victor said in the ringside as he was greeted with negative reactions from the crowd.
The British fighter got back to winning after his maiden career setback - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts felt Parker, thirty-one, merited the decision but the British boxer suffered the second defeat of his 28-fight career.
The Champion Secures Triumph in Slow Encounter
Buatsi's progress has plateaued in the past few years through contract problems and considerable time of inactivity.
Earlier forecast as the next star of UK boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a final roll of the dice - under fresh management.
He started carefully, with both competitors willing to take risks in a calculated opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after damaging his hand mid-fight, was participating in his second bout at light heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for the favorite, who utilized a solid defense to edge the more effective periods.
The crowd's patience decreased during regular grabbing, with Parker falling to the floor several times during grappling.
The underdog closed well, but multiple periods were challenging to assess. However, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just a single round.
Buatsi advances, but with the presence of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Motivates Manchester Derby Contest
In the secondary fight, Lyndon Arthur beat Rea by divided decision in a outstanding local rivalry fight to secure the European light heavyweight title.
The stadium grew hushed for a extremely emotional tribute ahead of the contest as 10 bells rang in honor of Manchester's own Ricky Hatton, who succumbed at age 46 in recently.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the last bell ended, the silence became a roar of "there's just one Hatton".
The competition inside the ropes matched the feeling. Arthur was floored by a powerful punch squarely on the jaw in the second round, rising shakily to his position on the eight count.
But the traditional red attire of Arthur soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was damaged quickly, noticeable damage developing under his eye as the fighters traded punishing blows.
Rea, twenty-seven, landed power punches but the champion, 34, matched the intensity with effective uppercuts as the pace hardly diminished over 12 rounds.
Arthur edged the result with official scores of draw, narrow lead and 115-112, but the two athletes were persistent and full of heart, everything their inspiration the legend stood for.
