UK light heavyweight Buatsi made a winning yet underwhelming start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a majority decision in a close ten-round fight at the Co-op Live Arena.
But the challenger had his moments, delivering effective single shots in a fight where the styles never quite clicked, with frequent clinching disrupting the action.
The scoring judges judged it 96-94 for to the winner, with the third a even score.
"It wasn't my finest showing but how do champions respond? They succeed," the victor commented in the arena as he was greeted with disapproval from the audience.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Various analysts thought the challenger, thirty-one, merited the decision but the contender suffered the second defeat of his 28-match career.
Buatsi Claims Triumph in Slow Encounter
His career development has plateaued in recent times through management issues and considerable time of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to realize his potential - maybe in what appears to be a last chance - under fresh management.
He started carefully, with both competitors willing to overcommit in a tentative early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was competing in only his second appearance at light heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for the favorite, who worked behind a protective stance to narrowly win the cleaner periods.
The audience's tolerance diminished because of frequent holding, with the challenger going down multiple occasions during grappling.
The underdog ended stronger, but several stanzas were hard to judge. Nevertheless, ex-champion the boxing analyst - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi progresses, but with the caliber of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Fuels Manchester Derby Fight
In the secondary fight, Arthur defeated Bradley Rea by close verdict in a outstanding local rivalry contest to capture the continental belt.
The venue became quiet for a deeply poignant tribute prior to the bout as a bell ceremony rang in remembrance of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the concluding sound faded, the quiet transitioned to a shout of "there's only one Ricky Hatton".
The competition within the ring matched the feeling. Arthur was sent to the canvas by a left hook flush on the jaw in the early round, rising shakily to his footing on the referee's count.
But the Manchester United-red attire of the fighter soon came forward again. On the opposite side, the opponent - in rival City blue - was damaged early, significant bruising appearing under his face as the pair landed powerful shots.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, responded in kind with effective uppercuts as the intensity hardly diminished over 12 rounds.
The victor barely secured the verdict with scoring tallies of draw, close margin and 115-112, but the two athletes were persistent and brave, all the qualities their inspiration the legend stood for.
