UK light-heavyweight Buatsi secured a victory yet disappointing debut to life under new promoters with a decision win over Zach Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a close ten-round contest at the Co-op Live Arena.
But Parker found success, connecting with powerful single shots in a contest where the techniques didn't complement each other, with frequent clinching spoiling the fight.
The officials had it 96-94 to the winner, with the third a 95-95.
"It wasn't my best display but how do champions respond? They win," the victor commented in the arena as he was faced disapproval from the audience.
The Londoner bounced back after his first professional defeat - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts felt the challenger, thirty-one, merited the victory but the British boxer experienced the second loss of his 28-match career.
Buatsi Secures Win in Slow Encounter
Buatsi's progress has stalled in recent times through contract problems and long spells of inactivity.
Earlier forecast as the next star of British boxing, he now is positioned trying to realize his potential - maybe in what appears to be a last chance - under recent support.
He began cautiously, with the two boxers prepared to be aggressive in a calculated early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second fight at light heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for Buatsi, who utilized a solid defense to narrowly win the more effective periods.
The spectators' acceptance wore thin amid frequent holding, with Parker slipping to the canvas various instances during close exchanges.
The underdog ended stronger, but several stanzas were hard to judge. However, ex-champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just only one stanza.
The victor moves on, but with the likes of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Memorial Inspires Manchester Derby Battle
In the co-main event, Lyndon Arthur defeated Bradley Rea by divided decision in a terrific all-Manchester battle to secure the European light heavyweight belt.
The arena fell silent for a deeply poignant homage before the fight as 10 bells rang in remembrance of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised match card in the city since Hatton's passing. As the concluding sound disappeared, the quiet gave way to a roar of "there's just one Hatton".
The competition during the bout matched the feeling. The eventual winner was sent to the canvas by a left hook squarely on the jaw in the early round, standing uncertainly to his footing on the referee's count.
But the traditional red shorts of Arthur soon came forward again. On the opposite side, the opponent - in opposing blue - was injured early, heavy swelling developing under his eye as the duo landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the pace seldom decreased over 12 rounds.
Arthur edged the decision with judges scorecards of 114-114, close margin and wider gap, but each competitor were relentless and courageous, exactly what their idol the legend stood for.
