British light heavyweight Buatsi made a winning yet disappointing debut to his career under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a close 10-round contest at the Co-op Live Arena.
But Parker had his moments, landing some telling single shots in a match where the techniques never quite clicked, with frequent clinching spoiling the fight.
Two judges had it 96-94 for to the winner, with the final judge a 95-95.
"It wasn't my finest performance but how do champions respond? They succeed," the victor said in the ringside as he was greeted with disapproval from the crowd.
The British fighter returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Various analysts thought Parker, thirty-one, deserved the decision but the British boxer endured the second defeat of his 28-bout career.
Buatsi Earns Triumph in Dull Encounter
His career development has plateaued in recent times through contract problems and long spells of inactivity.
Once tipped as the next star of UK boxing, he now finds himself trying to realize his potential - perhaps in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with the two boxers ready to be aggressive in a calculated opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was making just his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, creating difficulties for the favorite, who operated with a tight guard to edge the more effective stanzas.
The spectators' acceptance decreased during regular grabbing, with Parker slipping to the canvas multiple occasions during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. Although, previous titleholder Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the presence of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Tribute Fuels Local Rivalry Fight
In the supporting bout, Arthur defeated Rea by split-decision in a excellent all-Manchester contest to win the European light-heavyweight championship.
The stadium became quiet for a profoundly moving tribute ahead of the contest as ten bells sounded in honor of Manchester's own Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the concluding sound faded, the stillness gave way to a shout of "there's only one Hatton".
The action within the ring equaled the emotion. Arthur was floored by a powerful punch flush on the chin in the second round, getting up unsteadily to his footing on the count of eight.
But the red-colored attire of Arthur soon pressed ahead again. From the other corner, the opponent - in opposing blue - was marked up soon, noticeable damage forming under his face as the fighters exchanged powerful shots.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity hardly diminished over the full distance.
The victor edged the verdict with official scores of 114-114, narrow lead and wider gap, but each competitor were determined and full of heart, everything their idol Hatton embodied.
