UK light heavyweight Buatsi made a winning yet underwhelming start to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive 10-round fight at the Co-op Live Arena.
But Parker found success, delivering effective individual punches in a fight where the techniques never quite clicked, with constant grabbing spoiling the contest.
The scoring judges judged it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my greatest showing but what defines champions? They succeed," the victor commented in the ringside as he was met by disapproval from the audience.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Various analysts thought Parker, 31, deserved the victory but the British boxer suffered the second setback of his 28-fight career.
The Champion Earns Win in Uneventful Encounter
His career development has slowed in recent times through contract problems and extended periods of inactivity.
Previously predicted as the next star of the British fight scene, he now is positioned trying to realize his potential - perhaps in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with both competitors ready to take risks in a cagey early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second fight at light heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a tight guard to barely take the more effective stanzas.
The spectators' acceptance decreased during frequent holding, with Parker falling to the floor multiple occasions during clinches.
Parker closed well, but multiple periods were hard to judge. Although, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the presence of heavy hitter David Benavidez, and Russian star Bivol leading the category, the journey to titles - judging by this showing - still seems difficult.
Hatton Tribute Fuels Manchester Derby Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by split-decision in a excellent all-Manchester contest to secure the European light heavyweight title.
The venue fell silent for a deeply poignant tribute before the fight as ten bells tolled in honor of Manchester's own Hatton, who passed away 46 years old in September.
It was the premier televised match card in the location since Hatton's death. As the last bell faded, the stillness gave way to a shout of "there's just one Ricky Hatton".
The competition within the ring reflected the feeling. Arthur was knocked down by a significant blow squarely on the face in the second round, getting up unsteadily to his position on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. From the other corner, Rea - in rival City blue - was damaged quickly, heavy swelling developing under his eye as the duo landed punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace seldom decreased over 12 rounds.
The victor edged the verdict with scoring tallies of draw, narrow lead and clearer margin, but both fighters were determined and brave, everything their hero the legend represented.
