British light heavyweight Buatsi earned a win yet disappointing beginning to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a split decision in a tight ten-round bout at the boxing arena.
But the challenger found success, connecting with powerful individual punches in a match where the techniques failed to mesh, with constant grabbing spoiling the action.
The officials scored it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my best display but how do champions respond? They win," the victor said in the ring as he was met by boos from the audience.
The Londoner returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to secure a twentieth professional win.
Various analysts thought the challenger, 31, should have been awarded the win but the contender suffered the second defeat of his 28-bout career.
Buatsi Claims Victory in Uneventful Affair
His career development has stalled in recent years through management issues and long spells of inactivity.
Previously predicted as the next star of British boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with both competitors prepared to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second bout at light-heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for Buatsi, who operated with a tight guard to narrowly win the better periods.
The spectators' acceptance diminished amid frequent holding, with the challenger falling to the floor various instances during close exchanges.
The underdog closed well, but multiple periods were hard to judge. However, ex-champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Inspires Manchester Derby Fight
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a terrific local rivalry fight to capture the European light-heavyweight title.
The stadium grew hushed for a deeply poignant homage before the fight as ten bells sounded in remembrance of the city's native Ricky Hatton, who passed away 46 years old in recently.
It was the premier televised fight night in the urban center since Hatton's passing. As the final chime faded, the silence became a chant of "there's only one Ricky Hatton".
The competition during the bout matched the feeling. Arthur was knocked down by a left hook directly to the face in the initial stage, getting up unsteadily to his footing on the referee's count.
But the traditional red attire of Arthur soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was damaged early, noticeable damage forming under his eye as the fighters exchanged hard punches.
The challenger, 27, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the pace hardly diminished over twelve rounds.
The victor edged the decision with judges scorecards of 114-114, close margin and 115-112, but both fighters were persistent and courageous, everything their inspiration the legend represented.
