UK light heavyweight Buatsi earned a win yet unimpressive start to life under new promoters with a decision win over Zach Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a competitive ten-round contest at the boxing arena.
But Parker landed significant shots, connecting with powerful individual punches in a fight where the styles never quite clicked, with excessive holding spoiling the contest.
The scoring judges judged it 96-94 to the winner, with the third a 95-95.
"It wasn't my finest showing but what do champions do? They win," Buatsi said in the ringside as he was greeted with disapproval from the crowd.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Several boxing experts felt Parker, 31, merited the decision but the contender experienced the second loss of his 28-fight career.
Buatsi Earns Win in Dull Match
His career development has slowed in recent times through contract problems and considerable time of inactivity.
Previously predicted as the rising talent of the British fight scene, he now stands trying to realize his potential - possibly in what appears to be a last chance - under fresh management.
He began cautiously, with neither fighter prepared to take risks in a calculated early stages.
Parker, whose only previous defeat came at super middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was making just his second bout at the higher weight class.
By the halfway stage, Parker had kept it close, making life awkward for the favorite, who worked behind a tight guard to narrowly win the cleaner stanzas.
The spectators' acceptance wore thin because of frequent holding, with Parker slipping to the canvas various instances during clinches.
The underdog closed well, but several stanzas were difficult to score. Nevertheless, previous titleholder the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
The victor advances, but with the caliber of power puncher David Benavidez, and Russian star Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Hatton Homage Motivates Manchester Derby Battle
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a terrific local rivalry contest to capture the continental belt.
The arena fell silent for a profoundly moving memorial prior to the bout as a bell ceremony tolled in remembrance of the city's native Ricky Hatton, who passed away at age 46 in recently.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the last bell disappeared, the stillness transitioned to a chant of "there's only one Hatton".
The fighting inside the ropes equaled the feeling. Arthur was knocked down by a significant blow directly to the chin in the second round, getting up unsteadily to his feet on the eight count.
But the Manchester United-red shorts of Arthur soon came forward again. Across the ring, Rea - in opposing blue - was marked up quickly, noticeable damage forming under his orbital area as the pair exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with powerful upward punches as the pace seldom decreased over the full distance.
The victor barely secured the decision with official scores of even score, close margin and clearer margin, but the two athletes were determined and brave, all the qualities their inspiration the legend represented.
