UK light heavyweight Buatsi secured a victory yet underwhelming debut to life under recent management with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a tight 10-round bout at the boxing arena.
But the challenger had his moments, delivering effective clean blows in a fight where the styles didn't complement each other, with excessive holding spoiling the fight.
Two judges scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my best performance but what defines champions? They prevail," the victor commented in the ring as he was met by disapproval from the crowd.
The Londoner got back to winning after his first professional defeat - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Some ringside observers believed the challenger, thirty-one, deserved the win but the British boxer experienced the second setback of his 28-match professional journey.
Buatsi Claims Triumph in Slow Encounter
His career development has slowed in recent times through management issues and extended periods of inactivity.
Once tipped as the rising talent of UK boxing, he now stands trying to realize his potential - perhaps in what seems like a last chance - under recent support.
He started carefully, with the two boxers willing to be aggressive in a cagey opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second fight at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to edge the better rounds.
The spectators' acceptance decreased amid frequent holding, with Parker going down various instances during clinches.
Parker closed well, but many rounds were hard to judge. However, former world champion Carl Frampton - commentating on Dazn - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Fuels All-Manchester Battle
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a outstanding Manchester vs Manchester contest to capture the European light heavyweight belt.
The arena grew hushed for a profoundly moving tribute before the fight as a bell ceremony rang in remembrance of Manchester's own Ricky Hatton, who passed away at age 46 in September.
It was the first major televised fight night in the urban center since the passing of Hatton. As the last bell ended, the quiet gave way to a roar of "only one Ricky Hatton".
The action within the ring reflected the sentiment. The eventual winner was sent to the canvas by a left hook squarely on the chin in the initial stage, standing uncertainly to his feet on the referee's count.
But the red-colored equipment of Arthur soon pressed ahead again. From the other corner, the opponent - in opposing blue - was marked up soon, heavy swelling forming under his eye as the pair traded punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the intensity seldom decreased over twelve rounds.
The victor narrowly won the verdict with scoring tallies of even score, 115-113 and 115-112, but both fighters were determined and full of heart, all the qualities their hero the legend embodied.
