UK light-heavyweight Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a close 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling clean blows in a match where the techniques failed to mesh, with frequent clinching disrupting the fight.
Two judges judged it 96-94 to the winner, with the third a 95-95.
"It wasn't my best display but how do champions respond? They succeed," the victor said in the ring as he was met by boos from the spectators.
The British fighter got back to winning after his initial pro loss - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts felt Parker, thirty-one, deserved the victory but the contender endured the second defeat of his 28-bout career.
Buatsi Secures Victory in Uneventful Encounter
The fighter's advancement has stalled in the past few years through contract problems and considerable time of lack of fights.
Previously predicted as the future of UK boxing, he now stands trying to achieve expectations - possibly in what appears to be a last chance - under recent support.
He opened tentatively, with the two boxers willing to overcommit in a calculated initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after breaking his hand during the bout, was making just his second fight at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for the favorite, who utilized a solid defense to narrowly win the better rounds.
The crowd's patience wore thin amid regular grabbing, with the challenger going down several times during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just only one stanza.
Buatsi moves on, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Tribute Fuels Manchester Derby Battle
In the secondary fight, Lyndon Arthur defeated Rea by close verdict in a terrific local rivalry contest to win the European light heavyweight title.
The arena grew hushed for a profoundly moving homage ahead of the contest as ten bells tolled in honor of Manchester's own Ricky Hatton, who died at age 46 in recently.
It was the initial significant broadcast fight night in the city since Hatton's death. As the final chime disappeared, the quiet became a roar of "there's only one Hatton".
The competition inside the ropes matched the sentiment. The eventual winner was sent to the canvas by a significant blow squarely on the jaw in the second round, standing uncertainly to his feet on the count of eight.
But the red-colored shorts of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was injured quickly, heavy swelling developing under his orbital area as the pair landed punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with powerful upward punches as the action hardly diminished over the full distance.
Arthur narrowly won the result with official scores of draw, 115-113 and wider gap, but both fighters were relentless and full of heart, all the qualities their hero the legend stood for.
