British light-heavyweight Buatsi made a winning yet underwhelming start to life under fresh promotional backing with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a competitive ten-round bout at the Manchester venue.
But Parker had his moments, delivering effective clean blows in a contest where the techniques failed to mesh, with excessive holding marring the action.
The officials judged it 96-94 for to the winner, with the final judge 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 disapproval from the spectators.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in February - to earn a 20th career victory.
Several boxing experts felt the challenger, 31, should have been awarded the win but the British boxer suffered the second setback of his 28-bout professional journey.
The Champion Claims Triumph in Slow Match
The fighter's advancement has plateaued in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to realize his potential - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with both competitors prepared to take risks in a calculated initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in 2022 after breaking his hand during the bout, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a protective stance to narrowly win the more effective rounds.
The spectators' acceptance diminished because of frequent holding, with the challenger going down several times during grappling.
Parker ended stronger, but multiple periods were challenging to assess. However, ex-champion the boxing analyst - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor advances, but with the likes of hard hitter Benavidez, and Russian champion Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Homage Motivates Local Rivalry Fight
In the secondary fight, Arthur overcame Rea by divided decision in a terrific Manchester vs Manchester fight to capture the European light-heavyweight championship.
The arena grew hushed for a deeply poignant tribute before the fight as a bell ceremony sounded in remembrance of local hero Ricky Hatton, who passed away aged 46 in September.
It was the first major televised fight night in the city since Hatton's death. As the final chime disappeared, the quiet transitioned to a roar of "there's only one Hatton".
The competition within the ring matched the emotion. The eventual winner was sent to the canvas by a powerful punch squarely on the face in the initial stage, rising shakily to his footing on the eight count.
But the traditional red shorts of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was marked up early, noticeable damage forming under his face as the pair traded powerful shots.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with effective uppercuts as the intensity seldom decreased over 12 rounds.
The victor barely secured the decision with judges scorecards of even score, narrow lead and 115-112, but both fighters were determined and courageous, everything their idol the legend represented.
