UK light heavyweight Buatsi earned a win yet underwhelming beginning to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a split decision in a close ten-round fight at the Manchester venue.
But the challenger found success, connecting with powerful clean blows in a fight where the techniques didn't complement each other, with excessive holding marring the contest.
The officials scored it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my best display but how do champions respond? They win," Buatsi said in the arena as he was faced disapproval from the audience.
The Londoner got back to winning after his maiden career setback - an epic battle with his previous opponent in February - to secure a 20th career victory.
Some ringside observers felt the challenger, 31, should have been awarded the decision but the British boxer experienced the second setback of his 28-match professional journey.
Buatsi Secures Win in Uneventful Affair
The fighter's advancement has slowed in recent times through management issues and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to realize his potential - perhaps in what feels like a ultimate opportunity - under fresh management.
He started carefully, with the two boxers willing to be aggressive in a tentative early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was making just his second fight at light heavyweight.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who worked behind a solid defense to barely take the more effective rounds.
The crowd's patience diminished because of regular grabbing, with the challenger going down multiple occasions during close exchanges.
Parker ended stronger, but multiple periods were challenging to assess. However, ex-champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the presence of hard hitter David Benavidez, and Russian champion Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Memorial Motivates Local Rivalry Battle
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester battle to secure the European light heavyweight championship.
The arena grew hushed for a profoundly moving tribute prior to the bout as ten bells tolled in honor of Manchester's own Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast fight night in the city since Hatton's death. As the last bell ended, the stillness transitioned to a shout of "there's just one Ricky Hatton".
The action within the ring equaled the feeling. Arthur was floored by a significant blow squarely on the face in the early round, rising shakily to his feet on the count of eight.
But the Manchester United-red attire of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was injured quickly, noticeable damage appearing under his orbital area as the duo traded punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the pace seldom decreased over twelve rounds.
The victor barely secured the decision with judges scorecards of 114-114, narrow lead and 115-112, but the two athletes were determined and brave, everything their idol Hatton embodied.
