UK light heavyweight Buatsi made a winning yet underwhelming beginning to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a majority decision in a close 10-round fight at the Co-op Live Arena.
But Parker found success, landing some telling clean blows in a contest where the styles failed to mesh, with frequent clinching disrupting the fight.
The scoring judges had it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my finest performance but what do champions do? They win," Buatsi commented in the ring as he was faced disapproval from the crowd.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, should have been awarded the win but the British boxer suffered the second setback of his 28-match professional journey.
Buatsi Claims Triumph in Dull Encounter
The fighter's advancement has plateaued in the past few years through promotional disputes and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under fresh management.
He opened tentatively, with both competitors willing to be aggressive in a cagey initial rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after breaking his hand in the contest, was participating in his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, causing problems for the favorite, who utilized a tight guard to narrowly win the better stanzas.
The audience's tolerance decreased because of frequent holding, with the challenger going down various instances during grappling.
The underdog ended stronger, but several stanzas were hard to judge. Although, former world champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi progresses, but with the caliber of heavy hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Homage Inspires Local Rivalry Contest
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a excellent Manchester vs Manchester battle to capture the European light-heavyweight title.
The arena fell silent for a extremely emotional tribute prior to the bout as a bell ceremony rang in honor of local hero Ricky Hatton, who passed away aged 46 in recently.
It was the first major televised boxing event in the location since Hatton's death. As the last bell faded, the quiet gave way to a roar of "there's just one Hatton".
The competition inside the ropes equaled the sentiment. The eventual winner was knocked down by a powerful punch squarely on the jaw in the second round, standing uncertainly to his footing on the eight count.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, the opponent - in opposing blue - was injured quickly, significant bruising appearing under his face as the fighters landed hard punches.
The challenger, 27, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the action seldom decreased over twelve rounds.
Arthur edged the verdict with judges scorecards of draw, close margin and clearer margin, but each competitor were determined and courageous, exactly what their idol the legend embodied.
