British light-heavyweight Buatsi secured a victory yet unimpressive start to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a competitive ten-round bout at the Manchester venue.
But the challenger found success, connecting with powerful single shots in a match where the techniques failed to mesh, with constant grabbing disrupting the action.
The scoring judges judged it 96-94 to the winner, with the third a even score.
"It wasn't my best display but how do champions respond? They win," the victor said in the ring as he was met by boos from the audience.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Some ringside observers thought the challenger, 31, merited the decision but the British boxer experienced the second defeat of his 28-bout professional journey.
Buatsi Secures Win in Slow Encounter
Buatsi's progress has slowed in the past few years through contract problems and extended periods of inactivity.
Previously predicted as the future of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with both competitors willing to overcommit in a cagey initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after damaging his hand mid-fight, was participating in his second bout at light-heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who worked behind a protective stance to narrowly win the more effective rounds.
The audience's tolerance diminished amid frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
Parker finished the stronger, but many rounds were difficult to score. Although, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the caliber of heavy hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Hatton Memorial Motivates All-Manchester Contest
In the supporting bout, Arthur overcame Bradley Rea by divided decision in a terrific local rivalry fight to secure the continental title.
The arena fell silent for a profoundly moving homage before the fight as ten bells sounded in remembrance of the city's native Ricky Hatton, who died at age 46 in September.
It was the first major televised match card in the urban center since Hatton's passing. As the last bell ended, the stillness gave way to a chant of "there's only one Hatton".
The action during the bout matched the emotion. The eventual winner was sent to the canvas by a left hook directly to the chin in the second round, standing uncertainly to his position on the eight count.
But the red-colored equipment of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was marked up quickly, noticeable damage developing under his eye as the fighters exchanged punishing blows.
The challenger, 27, delivered effective strikes but the champion, 34, responded in kind with effective uppercuts as the action hardly diminished over 12 rounds.
The victor edged the result with judges scorecards of even score, close margin and 115-112, but both fighters were determined and full of heart, exactly what their hero Hatton embodied.
