British light heavyweight Buatsi secured a victory yet disappointing debut to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a majority decision in a close ten-round contest at the boxing arena.
But Parker landed significant shots, connecting with powerful single shots in a contest where the approaches failed to mesh, with excessive holding marring the contest.
Two judges judged it 96-94 to the winner, with the third a even score.
"It wasn't my finest display but how do champions respond? They prevail," the victor stated in the ring as he was faced negative reactions from the crowd.
The Londoner got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to claim a twentieth professional win.
Some ringside observers thought Parker, 31, should have been awarded the decision but the contender experienced the second defeat of his 28-match professional journey.
The Champion Secures Victory in Dull Match
Buatsi's progress has slowed in the past few years through contract problems and extended periods of inactivity.
Once tipped as the rising talent of UK boxing, he now stands trying to realize his potential - possibly in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors ready to take risks in a calculated opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in 2022 after breaking his hand during the bout, was participating in his second appearance at light heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for Buatsi, who operated with a protective stance to barely take the better rounds.
The audience's tolerance diminished amid regular grabbing, with the challenger going down multiple occasions during close exchanges.
Parker closed well, but multiple periods were challenging to assess. Although, ex-champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor advances, but with the presence of hard hitter Benavidez, and Russian champion Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Memorial Inspires Manchester Derby Contest
In the co-main event, Lyndon Arthur overcame Rea by divided decision in a outstanding local rivalry fight to win the European light-heavyweight championship.
The arena fell silent for a profoundly moving memorial prior to the bout as a bell ceremony rang in remembrance of local hero 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 stillness became a roar of "there's only one Hatton".
The action within the ring equaled the sentiment. Arthur was sent to the canvas by a significant blow squarely on the chin in the early round, standing uncertainly to his footing on the eight count.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was damaged quickly, noticeable damage appearing under his orbital area as the fighters landed powerful shots.
Rea, 27, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace seldom decreased over twelve rounds.
Arthur edged the verdict with scoring tallies of draw, narrow lead and 115-112, but each competitor were persistent and courageous, everything their inspiration Hatton represented.
