UK light heavyweight Buatsi made a winning yet unimpressive beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a split decision in a tight 10-round contest at the boxing arena.
But the challenger landed significant shots, delivering effective single shots in a fight where the approaches never quite clicked, with constant grabbing spoiling the contest.
Two judges had it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest display but how do champions respond? They prevail," the victor stated in the arena as he was faced negative reactions from the crowd.
The British fighter bounced back after his maiden career setback - an epic battle with his previous opponent in February - to earn a 20th pro success.
Some ringside observers believed the challenger, 31, merited the decision but the contender experienced the second setback of his 28-bout professional journey.
Buatsi Claims Win in Dull Affair
Buatsi's progress has stalled in the past few years through promotional disputes and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to realize his potential - maybe in what feels like a last chance - under recent support.
He began cautiously, with the two boxers willing to take risks in a calculated initial rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in 2022 after breaking his hand in the contest, was participating in his second fight at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for the favorite, who operated with a solid defense to edge the better periods.
The audience's tolerance decreased because of constant clinching, with the challenger slipping to the canvas various instances during grappling.
The underdog closed well, but multiple periods were difficult to score. However, previous titleholder Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor advances, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Hatton Tribute Motivates Manchester Derby Contest
In the co-main event, Arthur overcame Bradley Rea by divided decision in a outstanding all-Manchester fight to secure the continental title.
The stadium became quiet for a profoundly moving homage before the fight as 10 bells rang in remembrance of the city's native Ricky Hatton, who succumbed 46 years old in recently.
It was the first major televised boxing event in the city since the passing of Hatton. As the concluding sound faded, the silence became a chant of "there's only one Ricky Hatton".
The fighting inside the ropes reflected the sentiment. The eventual winner was floored by a left hook squarely on the chin in the early round, standing uncertainly to his position on the eight count.
But the traditional red shorts of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was marked up soon, heavy swelling developing under his face as the fighters traded powerful shots.
The challenger, 27, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the action rarely dropped over twelve rounds.
Arthur barely secured the decision with scoring tallies of 114-114, close margin and wider gap, but the two athletes were persistent and brave, exactly what their idol Hatton represented.
