UK light-heavyweight Buatsi secured a victory yet unimpressive debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a competitive ten-round fight at the boxing arena.
But Parker had his moments, connecting with powerful individual punches in a fight where the approaches didn't complement each other, with excessive holding spoiling the fight.
The scoring judges judged it 96-94 for to the winner, with the final judge a even score.
"It wasn't my best performance but what defines champions? They succeed," Buatsi commented in the ring as he was met by boos from the crowd.
The British fighter bounced back after his maiden career setback - an epic battle with Callum Smith in February - to earn a 20th pro success.
Some ringside observers felt the challenger, thirty-one, deserved the victory but the contender experienced the second setback of his 28-match career.
The Champion Secures Win in Uneventful Encounter
Buatsi's progress has slowed in the past few years through management issues and long spells of lack of fights.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to realize his potential - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, with neither fighter willing to overcommit in a tentative early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after damaging his hand mid-fight, was participating in his second fight at light-heavyweight.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who worked behind a protective stance to barely take the more effective rounds.
The spectators' acceptance decreased during frequent holding, with the challenger slipping to the canvas several times during grappling.
Parker closed well, but multiple periods were hard to judge. However, former world champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just one round.
Buatsi advances, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Homage Fuels Local Rivalry Battle
In the secondary fight, Arthur overcame Bradley Rea by split-decision in a terrific all-Manchester fight to secure the continental belt.
The arena fell silent for a extremely emotional memorial ahead of the contest as a bell ceremony sounded in memory of local hero Hatton, who succumbed at age 46 in last month.
It was the first major televised fight night in the urban center since Hatton's passing. As the last bell faded, the stillness gave way to a shout of "only one Ricky Hatton".
The competition within the ring matched the emotion. Arthur was sent to the canvas by a significant blow directly to the face in the initial stage, standing uncertainly to his feet on the referee's count.
But the traditional red equipment of Arthur 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 landed hard punches.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace rarely dropped over the full distance.
The victor edged the result with judges scorecards of draw, narrow lead and wider gap, but both fighters were persistent and full of heart, exactly what their idol the legend stood for.
