British light heavyweight Buatsi earned a win yet disappointing debut to his career under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a tight ten-round bout at the boxing arena.
But Parker found success, delivering effective single shots in a match where the styles failed to mesh, with constant grabbing marring the fight.
The scoring judges had it 96-94 in favor to the winner, with the third a even score.
"It wasn't my finest showing but how do champions respond? They win," Buatsi said in the ring as he was faced negative reactions from the crowd.
The Londoner bounced back after his maiden career setback - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, merited the win but the Derbyshire fighter suffered the second setback of his 28-match professional journey.
Buatsi Earns Triumph in Slow Encounter
His career development has slowed in the past few years through promotional disputes and extended periods of inactivity.
Once tipped as the next star of UK boxing, he now stands trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under recent support.
He opened tentatively, with neither fighter ready to be aggressive in a calculated initial rounds.
Parker, whose only previous defeat came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was making just his second appearance at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for the favorite, who worked behind a solid defense to barely take the more effective rounds.
The crowd's patience diminished because of constant clinching, with the challenger going down various instances during clinches.
Parker finished the stronger, but multiple periods were challenging to assess. Although, previous titleholder the boxing analyst - commentating on Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the caliber of heavy hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Tribute Fuels All-Manchester Fight
In the supporting bout, Arthur beat Bradley Rea by divided decision in a excellent all-Manchester battle to secure the European light heavyweight championship.
The venue fell silent for a extremely emotional homage before the fight as ten bells rang in memory of the city's native Ricky Hatton, who succumbed at age 46 in recently.
It was the premier televised boxing event in the location since Hatton's death. As the last bell faded, the stillness transitioned to a shout of "there's only one Ricky Hatton".
The action within the ring matched the sentiment. Arthur was sent to the canvas by a significant blow flush on the chin in the initial stage, rising shakily to his position on the eight count.
But the red-colored attire of Arthur soon came forward again. Across the ring, Rea - in opposing blue - was damaged early, heavy swelling forming under his orbital area as the duo landed hard punches.
The challenger, 27, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the action hardly diminished over the full distance.
Arthur edged the result with judges scorecards of draw, close margin and 115-112, but the two athletes were determined and courageous, exactly what their inspiration the legend stood for.
