UK light-heavyweight Buatsi made a winning yet disappointing beginning to his career under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a tight 10-round fight at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful single shots in a fight where the techniques failed to mesh, with constant grabbing disrupting the action.
Two judges judged it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my best showing but how do champions respond? They succeed," the victor commented in the ringside as he was faced boos from the audience.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in February - to secure a 20th pro success.
Various analysts felt the challenger, thirty-one, deserved the victory but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
Buatsi Secures Win in Dull Match
Buatsi's progress has slowed in the past few years through contract problems and long spells of lack of fights.
Once tipped as the future of British boxing, he now finds himself trying to realize his potential - possibly in what seems like a final roll of the dice - under recent support.
He started carefully, with both competitors willing to overcommit in a tentative opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after damaging his hand in the contest, was competing in only his second fight at the higher weight class.
By the halfway stage, Parker had made it competitive, causing problems for the favorite, who worked behind a tight guard to edge the cleaner stanzas.
The audience's tolerance decreased amid frequent holding, with the challenger falling to the floor several times during grappling.
Parker ended stronger, but multiple periods were hard to judge. However, previous titleholder Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the likes of power puncher David Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Tribute Fuels Manchester Derby Fight
In the co-main event, Arthur beat Bradley Rea by divided decision in a excellent local rivalry fight to secure the European light-heavyweight title.
The arena became quiet for a profoundly moving tribute ahead of the contest as a bell ceremony sounded in memory of local hero Hatton, who succumbed 46 years old in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the concluding sound ended, the quiet gave way to a roar of "only one Ricky Hatton".
The fighting during the bout reflected the feeling. Arthur was floored by a significant blow squarely on the jaw in the second round, standing uncertainly to his feet on the referee's count.
But the red-colored equipment of Arthur soon pressed ahead again. From the other corner, Rea - in competitive blue - was damaged soon, heavy swelling developing under his orbital area as the duo traded hard punches.
The challenger, 27, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the action hardly diminished over 12 rounds.
The victor narrowly won the decision with judges scorecards of draw, 115-113 and 115-112, but both fighters were persistent and courageous, all the qualities their hero Hatton stood for.
