UK light heavyweight Buatsi secured a victory yet unimpressive start to his career under recent management with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a close 10-round contest at the boxing arena.
But Parker landed significant shots, landing some telling individual punches in a fight where the techniques didn't complement each other, with excessive holding disrupting the action.
Two judges had it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best showing but how do champions respond? They win," Buatsi commented in the arena as he was greeted with boos from the crowd.
The British fighter bounced back after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts believed Parker, 31, merited the win but the British boxer endured the second defeat of his 28-fight career.
The Champion Earns Victory in Dull Match
The fighter's advancement has stalled in recent years through management issues and extended periods of inactivity.
Earlier forecast as the next star of British boxing, he now is positioned trying to achieve expectations - maybe in what seems like a last chance - under new promotional backing.
He opened tentatively, with neither fighter prepared to be aggressive in a tentative opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in 2022 after damaging his hand in the contest, was making just his second fight at the higher weight class.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who utilized a protective stance to narrowly win the cleaner periods.
The crowd's patience decreased because of constant clinching, with the challenger going down various instances during close exchanges.
Parker closed well, but several stanzas were hard to judge. Although, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just one round.
The victor progresses, but with the likes of power puncher Benavidez, and Russian star Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Tribute Fuels Local Rivalry Battle
In the secondary fight, Lyndon Arthur overcame Rea by close verdict in a outstanding local rivalry battle to secure the European light heavyweight championship.
The arena became quiet for a deeply poignant memorial ahead of the contest as a bell ceremony sounded in memory of the city's native Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the last bell disappeared, the silence transitioned to a shout of "there's only one Hatton".
The fighting within the ring matched the emotion. The eventual winner was floored by a significant blow squarely on the jaw in the second round, standing uncertainly to his footing on the count of eight.
But the red-colored attire of Arthur soon advanced again. From the other corner, the opponent - in opposing blue - was injured early, significant bruising developing under his orbital area as the duo landed hard punches.
Rea, 27, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity hardly diminished over 12 rounds.
The victor edged the result with scoring tallies of even score, narrow lead and wider gap, but both fighters were determined and brave, exactly what their idol Hatton stood for.
