UK light-heavyweight Buatsi secured a victory yet unimpressive beginning to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a majority decision in a tight ten-round bout at the boxing arena.
But the challenger landed significant shots, delivering effective individual punches in a match where the styles failed to mesh, with constant grabbing spoiling the contest.
The scoring judges judged it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my finest showing but what do champions do? They prevail," Buatsi said in the ringside as he was met by negative reactions from the audience.
The Londoner bounced back after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Various analysts believed the challenger, 31, merited the victory but the Derbyshire fighter endured the second loss of his 28-bout career.
The Champion Secures Victory in Dull Encounter
His career development has slowed in recent times through contract problems and extended periods of lack of fights.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers prepared to overcommit in a cagey initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was participating in his second fight at the higher weight class.
By the middle rounds, Parker had kept it close, making life awkward for the favorite, who worked behind a tight guard to barely take the better rounds.
The audience's tolerance decreased during regular grabbing, with the challenger falling to the floor various instances during close exchanges.
The underdog ended stronger, but several stanzas were hard to judge. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of hard hitter David Benavidez, and Russian champion Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Inspires Local Rivalry Contest
In the co-main event, Lyndon Arthur beat Rea by close verdict in a outstanding local rivalry contest to secure the European light heavyweight championship.
The venue became quiet for a profoundly moving tribute ahead of the contest as ten bells sounded in honor of local hero Hatton, who passed away aged 46 in September.
It was the premier televised match card in the city since Hatton's death. As the final chime faded, the quiet transitioned to a chant of "there's just one Ricky Hatton".
The competition during the bout reflected the emotion. Arthur was floored by a significant blow flush on the face in the early round, getting up unsteadily to his footing on the referee's count.
But the traditional red equipment of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was marked up soon, noticeable damage forming under his face as the duo landed powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity hardly diminished over the full distance.
The victor barely secured the decision with scoring tallies of draw, close margin and 115-112, but each competitor were relentless and courageous, everything their inspiration Hatton embodied.
