UK light heavyweight Buatsi earned a win yet disappointing debut to life under new promoters 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 close ten-round contest at the Manchester venue.
But the challenger had his moments, delivering effective clean blows in a contest where the techniques never quite clicked, with excessive holding disrupting the action.
The officials had it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They prevail," Buatsi said in the arena as he was met by negative reactions from the spectators.
The British fighter bounced back after his initial pro loss - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Various analysts felt the challenger, 31, merited the victory but the Derbyshire fighter endured the second defeat of his 28-bout career.
The Champion Claims Win in Dull Encounter
Buatsi's progress has plateaued in recent times through contract problems and considerable time of inactivity.
Earlier forecast as the next star of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers ready to be aggressive in a calculated opening few rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after damaging his hand mid-fight, was participating in his second bout at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, causing problems for the favorite, who operated with a protective stance to narrowly win the cleaner periods.
The spectators' acceptance wore thin amid regular grabbing, with Parker falling to the floor various instances during clinches.
Parker ended stronger, but several stanzas were hard to judge. Although, former world champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just one round.
The victor advances, but with the caliber of power puncher David Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Homage Fuels Local Rivalry Battle
In the secondary fight, Arthur overcame Bradley Rea by divided decision in a terrific Manchester vs Manchester contest to capture the European light heavyweight belt.
The arena fell silent for a extremely emotional tribute ahead of the contest as a bell ceremony sounded in memory of local hero Ricky Hatton, who died at age 46 in September.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the final chime disappeared, the silence became a shout of "only one Hatton".
The fighting inside the ropes matched the feeling. Arthur was floored by a significant blow directly to the face in the initial stage, rising shakily to his footing on the count of eight.
But the traditional red attire of the fighter soon came forward again. Across the ring, the opponent - in competitive blue - was injured quickly, heavy swelling appearing under his eye as the duo traded hard punches.
Rea, 27, connected with strong blows but the champion, 34, matched the intensity with effective uppercuts as the action rarely dropped over twelve rounds.
Arthur edged the decision with scoring tallies of even score, close margin and wider gap, but the two athletes were determined and courageous, exactly what their idol Hatton embodied.
