UK light-heavyweight Buatsi made a winning yet unimpressive beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a competitive 10-round bout at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a match where the approaches didn't complement each other, with frequent clinching spoiling the fight.
Two judges judged it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my best performance but what defines champions? They prevail," the victor commented in the arena as he was greeted with negative reactions from the crowd.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Various analysts believed Parker, thirty-one, merited the decision but the Derbyshire fighter endured the second setback of his 28-match professional journey.
Buatsi Claims Win in Slow Match
His career development has slowed in the past few years through management issues and long spells of lack of fights.
Previously predicted as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with the two boxers prepared to take risks in a calculated early stages.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was participating in his second fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who operated with a protective stance to barely take the cleaner rounds.
The audience's tolerance wore thin because of regular grabbing, with the challenger falling to the floor several times during clinches.
Parker ended stronger, but multiple periods were hard to judge. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the caliber of heavy hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Tribute Inspires Manchester Derby Fight
In the supporting bout, Arthur defeated Rea by close verdict in a outstanding all-Manchester battle to capture the European light heavyweight belt.
The stadium became quiet for a extremely emotional homage ahead of the contest as a bell ceremony sounded in memory of the city's native Ricky Hatton, who passed away at age 46 in last month.
It was the premier televised boxing event in the location since Hatton's death. As the last bell faded, the quiet transitioned to a shout of "there's only one Hatton".
The competition within the ring matched the sentiment. The eventual winner was sent to the canvas by a left hook squarely on the jaw in the early round, getting up unsteadily to his footing on the referee's count.
But the red-colored shorts of Arthur soon came forward again. From the other corner, the opponent - in rival City blue - was marked up soon, noticeable damage forming under his face as the duo exchanged punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with powerful upward punches as the intensity seldom decreased over 12 rounds.
The victor edged the verdict with scoring tallies of even score, 115-113 and 115-112, but each competitor were persistent and brave, exactly what their idol the legend embodied.
