British light-heavyweight Buatsi earned a win yet unimpressive beginning to life under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a majority decision in a close 10-round bout at the Manchester venue.
But Parker had his moments, landing some telling clean blows in a match where the techniques never quite clicked, with frequent clinching disrupting the fight.
Two judges had it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my finest showing but what defines champions? They prevail," Buatsi commented in the ring as he was met by disapproval from the audience.
The Londoner bounced back after his maiden career setback - an memorable fight with his previous opponent in February - to earn a 20th career victory.
Various analysts felt Parker, thirty-one, merited the win but the British boxer suffered the second defeat of his 28-bout career.
The Champion Claims Victory in Uneventful Encounter
The fighter's advancement has slowed in the past few years through promotional disputes and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to realize his potential - maybe in what seems like a last chance - under fresh management.
He started carefully, with the two boxers willing to be aggressive in a calculated opening few rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in 2022 after suffering a hand injury mid-fight, was participating in his second fight at light-heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for the favorite, who utilized a solid defense to narrowly win the better stanzas.
The crowd's patience diminished during frequent holding, with Parker falling to the floor multiple occasions during clinches.
The underdog finished the stronger, but multiple periods were difficult to score. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, giving Buatsi just a single round.
Buatsi advances, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Homage Inspires All-Manchester Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a outstanding local rivalry battle to capture the European light heavyweight title.
The stadium became quiet for a profoundly moving tribute before the fight as 10 bells tolled in remembrance of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised fight night in the location since the passing of Hatton. As the concluding sound ended, the stillness gave way to a roar of "there's just one Hatton".
The action inside the ropes reflected the sentiment. The eventual winner was floored by a powerful punch squarely on the chin in the early round, getting up unsteadily to his footing on the eight count.
But the Manchester United-red attire of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was injured quickly, significant bruising forming under his face as the pair landed hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the pace hardly diminished over 12 rounds.
Arthur edged the decision with scoring tallies of even score, close margin and clearer margin, but each competitor were persistent and full of heart, all the qualities their idol the legend embodied.
