British light-heavyweight Buatsi made a winning yet disappointing beginning to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a tight 10-round fight at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a match where the styles failed to mesh, with constant grabbing marring the fight.
The officials judged it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my greatest display but what do champions do? They win," Buatsi commented in the ring as he was faced boos from the audience.
The British fighter bounced back after his first professional defeat - an memorable fight with his previous opponent in last winter - to earn a 20th career victory.
Several boxing experts thought the challenger, thirty-one, should have been awarded the decision but the British boxer endured the second setback of his 28-match career.
Buatsi Secures Win in Dull Match
His career development has plateaued in recent times through promotional disputes and extended periods of lack of fights.
Previously predicted as the rising talent of British boxing, he now finds himself trying to realize his potential - perhaps in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with neither fighter willing to take risks in a calculated early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after damaging his hand in the contest, was competing in only his second appearance at light heavyweight.
By the middle rounds, Parker had kept it close, causing problems for Buatsi, who operated with a solid defense to edge the more effective rounds.
The spectators' acceptance decreased amid regular grabbing, with Parker slipping to the canvas multiple occasions during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. Nevertheless, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the likes of power puncher David Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Memorial Inspires Manchester Derby Battle
In the secondary fight, Lyndon Arthur beat Rea by divided decision in a terrific Manchester vs Manchester battle to capture the European light heavyweight title.
The venue became quiet for a extremely emotional homage before the fight as ten bells sounded in remembrance of the city's native Hatton, who passed away 46 years old in last month.
It was the premier televised match card in the city since Hatton's passing. As the concluding sound ended, the stillness transitioned to a roar of "there's only one Ricky Hatton".
The competition during the bout equaled the emotion. Arthur was knocked down by a significant blow flush on the jaw in the initial stage, rising shakily to his position on the referee's count.
But the traditional red equipment of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was injured soon, significant bruising developing under his orbital area as the pair exchanged hard punches.
The challenger, 27, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the intensity hardly diminished over twelve rounds.
The victor barely secured the decision with official scores of draw, close margin and wider gap, but both fighters were relentless and brave, everything their idol Hatton represented.
