UK light heavyweight Buatsi secured a victory yet underwhelming debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close 10-round bout at the boxing arena.
But the challenger landed significant shots, delivering effective single shots in a fight where the techniques failed to mesh, with excessive holding disrupting the action.
Two judges judged it 96-94 for to the winner, with the final judge a even score.
"It wasn't my best performance but what defines champions? They succeed," Buatsi said in the ring as he was met by disapproval from the audience.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers thought the challenger, thirty-one, deserved the win but the Derbyshire fighter endured the second loss of his 28-fight professional journey.
Buatsi Claims Win in Dull Match
Buatsi's progress has stalled in the past few years through contract problems and long spells of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to achieve expectations - maybe in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers 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 suffering a hand injury in the contest, was competing in only his second fight at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a solid defense to barely take the better periods.
The crowd's patience diminished amid regular grabbing, with Parker falling to the floor several times during clinches.
The underdog closed well, but multiple periods were challenging to assess. Although, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Hatton Homage Fuels Local Rivalry Fight
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding Manchester vs Manchester contest to secure the European light heavyweight championship.
The venue fell silent for a extremely emotional tribute before the fight as ten bells rang in remembrance of the city's native Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the last bell faded, the stillness gave way to a shout of "there's just one Hatton".
The fighting during the bout equaled the emotion. Arthur was floored by a left hook squarely on the jaw in the early round, standing uncertainly to his footing on the referee's count.
But the Manchester United-red shorts of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was injured quickly, heavy swelling forming under his orbital area as the fighters traded punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over twelve rounds.
Arthur narrowly won the decision with official scores of draw, narrow lead and wider gap, but both fighters were relentless and full of heart, all the qualities their inspiration the legend represented.
