British light heavyweight Buatsi secured a victory yet unimpressive beginning to his career under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a tight 10-round bout at the Co-op Live Arena.
But Parker found success, delivering effective clean blows in a contest where the approaches never quite clicked, with excessive holding spoiling the fight.
Two judges judged it 96-94 to the winner, with the third a even score.
"It wasn't my finest showing but what defines champions? They prevail," Buatsi said in the ringside as he was met by boos from the audience.
The British fighter got back to winning after his first professional defeat - an epic battle with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers felt Parker, 31, deserved the win but the British boxer experienced the second loss of his 28-match professional journey.
Buatsi Claims Win in Uneventful Encounter
Buatsi's progress has stalled in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what appears to be a last chance - under fresh management.
He opened tentatively, with the two boxers willing to overcommit in a cagey opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second bout at the higher weight class.
By the halfway stage, Parker had stayed in contention, making life awkward for the favorite, who utilized a solid defense to edge the more effective rounds.
The audience's tolerance decreased during constant clinching, with the challenger falling to the floor various instances during close exchanges.
The underdog ended stronger, but many rounds were difficult to score. However, previous titleholder the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
The victor progresses, but with the caliber of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Hatton Homage Fuels All-Manchester Fight
In the supporting bout, Lyndon Arthur beat Rea by split-decision in a terrific local rivalry fight to secure the continental title.
The arena became quiet for a profoundly moving homage before the fight as 10 bells rang in remembrance of Manchester's own Hatton, who passed away at age 46 in last month.
It was the premier televised match card in the city since Hatton's death. As the final chime ended, the silence gave way to a roar of "there's just one Hatton".
The fighting within the ring matched the emotion. Arthur was floored by a significant blow flush on the face in the initial stage, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was injured quickly, heavy swelling forming under his face as the duo traded powerful shots.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with powerful upward punches as the pace hardly diminished over 12 rounds.
Arthur barely secured the result with official scores of draw, close margin and 115-112, but the two athletes were relentless and courageous, exactly what their idol Hatton embodied.
