UK light heavyweight Buatsi made a winning yet disappointing start to his career under fresh promotional backing with a decision win over Zach Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a judges' verdict in a competitive 10-round contest at the Co-op Live Arena.
But the challenger found success, delivering effective clean blows in a contest where the techniques didn't complement each other, with frequent clinching marring the contest.
Two judges scored it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best display but how do champions respond? They succeed," the victor stated in the arena as he was met by boos from the crowd.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts felt the challenger, 31, deserved the decision but the Derbyshire fighter suffered the second setback of his 28-match career.
Buatsi Earns Victory in Slow Encounter
Buatsi's progress has stalled in recent years through management issues and long spells of lack of fights.
Once tipped as the next star of the British fight scene, he now stands trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, with both competitors willing to be aggressive in a tentative opening few rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after damaging his hand during the bout, was making just his second bout at light heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for the favorite, who operated with a solid defense to barely take the cleaner periods.
The audience's tolerance wore thin because of frequent holding, with the challenger falling to the floor various instances during grappling.
The underdog ended stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it particularly wide for Parker, giving Buatsi just a single round.
The victor progresses, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Homage Motivates Manchester Derby Battle
In the secondary fight, Arthur beat Rea by close verdict in a outstanding Manchester vs Manchester contest to secure the continental belt.
The stadium became quiet for a deeply poignant homage before the fight as ten bells sounded in memory of Manchester's own Hatton, who died at age 46 in last month.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the final chime disappeared, the quiet became a shout of "only one Ricky Hatton".
The action inside the ropes equaled the feeling. The eventual winner was sent to the canvas by a significant blow squarely on the jaw in the initial stage, rising shakily to his footing on the referee's count.
But the traditional red shorts of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was marked up early, noticeable damage developing under his eye as the pair exchanged hard punches.
Rea, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the pace hardly diminished over the full distance.
Arthur edged the decision with official scores of draw, narrow lead and wider gap, but both fighters were relentless and brave, all the qualities their inspiration Hatton represented.
