British light-heavyweight Buatsi earned a win yet underwhelming start to life under new promoters 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 close ten-round contest at the Co-op Live Arena.
But the challenger found success, landing some telling clean blows in a fight where the approaches never quite clicked, with excessive holding marring the action.
The officials scored it 96-94 to the winner, with the third a even score.
"It wasn't my best display but what defines champions? They succeed," Buatsi stated in the ringside as he was met by boos from the spectators.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to earn a twentieth professional win.
Various analysts believed Parker, thirty-one, deserved the victory but the Derbyshire fighter suffered the second setback of his 28-match professional journey.
The Champion Secures Win in Dull Encounter
The fighter's advancement has stalled in recent times through promotional disputes and long spells of lack of fights.
Earlier forecast as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, with neither fighter prepared to take risks in a tentative initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for the favorite, who operated with a tight guard to narrowly win the better stanzas.
The audience's tolerance wore thin amid regular grabbing, with Parker falling to the floor several times during close exchanges.
Parker ended stronger, but many rounds were difficult to score. Nevertheless, previous titleholder Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
The victor advances, but with the likes of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - judging by this showing - still seems difficult.
Hatton Tribute Motivates All-Manchester Battle
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a outstanding Manchester vs Manchester fight to secure the European light-heavyweight belt.
The arena grew hushed for a deeply poignant tribute ahead of the contest as ten bells tolled in memory of local hero Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast match card in the city since Hatton's death. As the final chime disappeared, the quiet became a chant of "there's only one Hatton".
The fighting within the ring reflected the emotion. The eventual winner was floored by a powerful punch flush on the face in the initial stage, standing uncertainly to his feet on the eight count.
But the red-colored equipment of Arthur soon advanced again. From the other corner, the opponent - in rival City blue - was injured soon, noticeable damage appearing under his eye as the fighters exchanged powerful shots.
The challenger, 27, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the action seldom decreased over 12 rounds.
The victor narrowly won the decision with official scores of draw, 115-113 and clearer margin, but the two athletes were determined and brave, everything their inspiration the legend embodied.
