British light-heavyweight Buatsi made a winning yet disappointing start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a competitive ten-round contest at the Manchester venue.
But Parker had his moments, connecting with powerful clean blows in a fight where the styles failed to mesh, with constant grabbing disrupting the contest.
Two judges had it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my best display but how do champions respond? They win," the victor commented in the ring as he was faced boos from the crowd.
The Londoner got back to winning after his first professional defeat - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Some ringside observers thought the challenger, thirty-one, deserved the victory but the contender suffered the second setback of his 28-match career.
Buatsi Earns Triumph in Slow Encounter
The fighter's advancement has plateaued in recent times through contract problems and considerable time of inactivity.
Previously predicted as the future of UK boxing, he now finds himself trying to realize his potential - possibly in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors willing to be aggressive in a calculated early stages.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand during the bout, was participating in his second appearance at light-heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for Buatsi, who operated with a solid defense to narrowly win the more effective stanzas.
The audience's tolerance wore thin amid frequent holding, with Parker going down various instances during close exchanges.
Parker ended stronger, but several stanzas were hard to judge. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of hard hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - based on this performance - still appears challenging.
Hatton Homage Inspires Manchester Derby Contest
In the secondary fight, Arthur overcame Rea by divided decision in a excellent Manchester vs Manchester fight to capture the European light heavyweight championship.
The arena fell silent for a deeply poignant tribute before the fight as a bell ceremony sounded in honor of the city's native Hatton, who succumbed aged 46 in September.
It was the premier televised fight night in the urban center since Hatton's death. As the final chime ended, the silence became a roar of "there's only one Hatton".
The action during the bout matched the emotion. The eventual winner was floored by a significant blow flush on the jaw in the initial stage, rising shakily to his feet on the referee's count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was marked up early, heavy swelling developing under his orbital area as the pair landed punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the pace seldom decreased over the full distance.
Arthur barely secured the result with official scores of 114-114, 115-113 and clearer margin, but each competitor were persistent and courageous, exactly what their idol the legend embodied.
