UK light heavyweight Buatsi made a winning yet underwhelming debut to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a majority decision in a competitive 10-round bout at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a fight where the techniques never quite clicked, with frequent clinching spoiling the action.
The officials had it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my best display but how do champions respond? They succeed," Buatsi commented in the arena as he was faced boos from the crowd.
The Londoner got back to winning after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a 20th pro success.
Various analysts felt the challenger, thirty-one, deserved the victory but the Derbyshire fighter suffered the second defeat of his 28-fight career.
Buatsi Earns Win in Dull Affair
Buatsi's progress has slowed in recent years through contract problems and extended periods of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under recent support.
He started carefully, with both competitors prepared to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second fight at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a protective stance to narrowly win the cleaner rounds.
The audience's tolerance diminished amid regular grabbing, with Parker slipping to the canvas multiple occasions during grappling.
The underdog closed well, but multiple periods were difficult to score. Although, former world champion the boxing analyst - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor advances, but with the likes of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Hatton Memorial Inspires All-Manchester Contest
In the supporting bout, Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester contest to win the European light-heavyweight title.
The venue grew hushed for a profoundly moving tribute ahead of the contest as a bell ceremony rang in honor of Manchester's own Hatton, who succumbed 46 years old in last month.
It was the first major televised fight night in the urban center since the passing of Hatton. As the final chime ended, the silence became a chant of "only one Hatton".
The fighting within the ring matched the sentiment. Arthur was sent to the canvas by a powerful punch flush on the face in the initial stage, standing uncertainly to his position on the referee's count.
But the red-colored shorts of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was marked up early, heavy swelling appearing under his eye as the pair exchanged powerful shots.
The challenger, 27, landed power punches but the champion, thirty-four, matched the intensity with powerful upward punches as the intensity rarely dropped over 12 rounds.
Arthur barely secured the result with judges scorecards of draw, close margin and clearer margin, but each competitor were persistent and brave, everything their hero the legend embodied.
