UK light-heavyweight Buatsi earned a win yet disappointing start to his career 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 competitive 10-round contest at the boxing arena.
But Parker landed significant shots, landing some telling individual punches in a match where the techniques didn't complement each other, with constant grabbing spoiling the contest.
Two judges judged it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my greatest display but how do champions respond? They win," Buatsi commented in the ring as he was faced negative reactions from the crowd.
The British fighter bounced back after his first professional defeat - an epic battle with his previous opponent in February - to claim a 20th pro success.
Various analysts thought Parker, 31, should have been awarded the win but the Derbyshire fighter endured the second loss of his 28-bout career.
Buatsi Claims Win in Dull Encounter
His career development has stalled in the past few years through management issues and long spells of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to achieve expectations - possibly in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with both competitors willing to overcommit in a tentative initial rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in 2022 after suffering a hand injury during the bout, was competing in only his second fight at light-heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a solid defense to narrowly win the cleaner periods.
The spectators' acceptance wore thin during frequent holding, with Parker going down multiple occasions during grappling.
The underdog ended stronger, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
The victor moves on, but with the likes of power puncher David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Memorial Motivates Manchester Derby Contest
In the supporting bout, Arthur overcame Rea by close verdict in a terrific local rivalry battle to capture the continental belt.
The venue fell silent for a deeply poignant memorial prior to the bout as a bell ceremony rang in memory of the city's native Ricky Hatton, who died 46 years old in September.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the final chime disappeared, the quiet became a shout of "there's just one Ricky Hatton".
The action during the bout reflected the sentiment. The eventual winner was floored by a left hook flush on the jaw in the second round, standing uncertainly to his position on the eight count.
But the traditional red attire of the fighter soon advanced again. From the other corner, the opponent - in competitive blue - was injured soon, significant bruising developing under his face as the duo exchanged powerful shots.
Rea, 27, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the intensity rarely dropped over 12 rounds.
The victor narrowly won the result with official scores of even score, close margin and 115-112, but the two athletes were relentless and brave, exactly what their idol the legend represented.
