British light heavyweight Buatsi earned a win yet disappointing start to his career under new promoters with a points victory over Zach Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a close 10-round fight at the Manchester venue.
But Parker found success, delivering effective individual punches in a fight where the techniques failed to mesh, with constant grabbing spoiling the action.
The officials scored it 96-94 to Buatsi, with the third a even score.
"It wasn't my greatest showing but what defines champions? They prevail," the victor stated in the ringside as he was faced boos from the audience.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a 20th career victory.
Various analysts believed the challenger, thirty-one, merited the win but the contender endured the second loss of his 28-bout career.
Buatsi Claims Victory in Dull Encounter
The fighter's advancement has stalled in the past few years through promotional disputes and considerable time of lack of fights.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what seems like a last chance - under fresh management.
He started carefully, with neither fighter ready to overcommit in a tentative early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in 2022 after breaking his hand mid-fight, was making just his second fight at the higher weight class.
By the fight's midpoint, Parker had made it competitive, causing problems for the favorite, who utilized a solid defense to barely take the cleaner periods.
The audience's tolerance decreased because of regular grabbing, with the challenger slipping to the canvas several times during clinches.
Parker ended stronger, but multiple periods were difficult to score. However, previous titleholder the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Russian star Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Fuels Manchester Derby Battle
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a excellent all-Manchester battle to capture the continental belt.
The venue became quiet for a extremely emotional homage prior to the bout as 10 bells tolled in memory of the city's native Hatton, who died aged 46 in last month.
It was the first major televised boxing event in the city since Hatton's passing. As the concluding sound faded, the quiet became a chant of "only one Hatton".
The action inside the ropes reflected the feeling. Arthur was knocked down by a significant blow directly to the jaw in the early round, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red attire of the fighter soon pressed ahead again. From the other corner, Rea - in rival City blue - was injured early, noticeable damage appearing under his face as the fighters traded punishing blows.
The challenger, 27, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the intensity hardly diminished over 12 rounds.
Arthur narrowly won the verdict with judges scorecards of even score, close margin and 115-112, but the two athletes were determined and full of heart, all the qualities their hero the legend represented.
