UK light-heavyweight Buatsi secured a victory yet unimpressive debut to his career under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a split decision in a close ten-round bout at the Co-op Live Arena.
But Parker found success, delivering effective individual punches in a match where the styles never quite clicked, with constant grabbing spoiling the action.
Two judges had it 96-94 for to the winner, with the third a even score.
"It wasn't my best showing but what do champions do? They prevail," the victor commented in the ringside as he was greeted with boos from the audience.
The Londoner got back to winning after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a 20th career victory.
Various analysts felt the challenger, thirty-one, deserved the decision but the British boxer endured the second defeat of his 28-fight career.
The Champion Claims Triumph in Slow Affair
Buatsi's progress has slowed in recent times through promotional disputes and considerable time of inactivity.
Once tipped as the rising talent of UK boxing, he now finds himself trying to achieve expectations - possibly in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter prepared to take risks in a tentative initial rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand mid-fight, was making just his second fight at light heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for the favorite, who worked behind a protective stance to barely take the better rounds.
The crowd's patience wore thin during constant clinching, with Parker falling to the floor several times during grappling.
The underdog ended stronger, but multiple periods were challenging to assess. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, giving Buatsi just one round.
The victor moves on, but with the presence of heavy hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Hatton Homage Motivates All-Manchester Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a terrific local rivalry contest to capture the European light-heavyweight championship.
The venue fell silent for a profoundly moving homage before the fight as a bell ceremony sounded in remembrance of Manchester's own Ricky Hatton, who died at age 46 in last month.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the final chime disappeared, the silence transitioned to a chant of "only one Hatton".
The fighting within the ring matched the emotion. Arthur was sent to the canvas by a left hook flush on the jaw in the early round, rising shakily to his feet on the count of eight.
But the traditional red attire of Arthur soon pressed ahead again. From the other corner, Rea - in opposing blue - was damaged soon, significant bruising developing under his eye as the duo traded powerful shots.
Rea, 27, connected with strong blows but the champion, thirty-four, responded in kind with stinging uppercuts as the pace hardly diminished over 12 rounds.
The victor narrowly won the result with judges scorecards of even score, narrow lead and clearer margin, but both fighters were persistent and full of heart, exactly what their hero Hatton stood for.
