British light heavyweight Buatsi made a winning yet unimpressive beginning to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a split decision in a tight ten-round bout at the boxing arena.
But Parker had his moments, delivering effective single shots in a fight where the approaches never quite clicked, with excessive holding marring the fight.
The officials had it 96-94 for to Buatsi, with the third a even score.
"It wasn't my best display but what defines champions? They win," Buatsi said in the ringside as he was greeted with boos from the crowd.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to earn a 20th pro success.
Several boxing experts felt Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter suffered the second defeat of his 28-bout career.
Buatsi Claims Victory in Dull Encounter
The fighter's advancement has plateaued in recent times through promotional disputes and long spells of inactivity.
Previously predicted as the future of UK boxing, he now is positioned trying to achieve expectations - maybe in what feels like a final roll of the dice - under recent support.
He began cautiously, with the two boxers prepared to take risks in a cagey opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was making just his second bout at the higher weight class.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who utilized a protective stance to narrowly win the more effective stanzas.
The spectators' acceptance decreased because of frequent holding, with Parker going down multiple occasions during grappling.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, ex-champion the boxing analyst - commentating on Dazn - had it strongly leaning for the challenger, giving Buatsi just one round.
The victor advances, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Inspires All-Manchester Battle
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a terrific Manchester vs Manchester fight to win the European light heavyweight title.
The stadium grew hushed for a profoundly moving homage ahead of the contest as a bell ceremony sounded in memory of the city's native Hatton, who succumbed at age 46 in last month.
It was the premier televised fight night in the location since the passing of Hatton. As the last bell faded, the quiet gave way to a shout of "only one Ricky Hatton".
The action inside the ropes equaled the emotion. Arthur was floored by a left hook directly to the face in the second round, standing uncertainly to his footing on the eight count.
But the traditional red shorts of Arthur soon advanced again. Across the ring, Rea - in competitive blue - was marked up soon, significant bruising forming under his face as the duo traded punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the action hardly diminished over 12 rounds.
Arthur narrowly won the result with scoring tallies of draw, 115-113 and 115-112, but both fighters were determined and courageous, exactly what their idol the legend stood for.
