UK light-heavyweight Buatsi secured a victory yet underwhelming start to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a split decision in a close 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling clean blows in a contest where the styles failed to mesh, with excessive holding marring the fight.
The officials scored it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my finest showing but what do champions do? They succeed," the victor commented in the ringside as he was greeted with negative reactions from the crowd.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers felt Parker, thirty-one, merited the win but the Derbyshire fighter experienced the second setback of his 28-match professional journey.
The Champion Secures Win in Slow Encounter
His career development has slowed in recent years through management issues and considerable time of inactivity.
Previously predicted as the rising talent of British boxing, he now finds himself trying to achieve expectations - possibly in what feels like a last chance - under fresh management.
He opened tentatively, with neither fighter prepared to take risks in a tentative opening few rounds.
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 participating in his second appearance at light-heavyweight.
By the middle rounds, Parker had made it competitive, creating difficulties for the favorite, who utilized a tight guard to edge the more effective stanzas.
The audience's tolerance wore thin amid regular grabbing, with Parker falling to the floor various instances during close exchanges.
The underdog ended stronger, but many rounds were challenging to assess. Nevertheless, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the caliber of heavy hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Tribute Motivates Manchester Derby Fight
In the supporting bout, Lyndon Arthur beat Rea by divided decision in a outstanding local rivalry fight to win the continental belt.
The venue grew hushed for a profoundly moving tribute prior to the bout as a bell ceremony tolled in honor of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the first major televised fight night in the urban center since the passing of Hatton. As the last bell disappeared, the stillness became a shout of "there's just one Ricky Hatton".
The fighting during the bout equaled the emotion. Arthur was sent to the canvas by a significant blow flush on the face in the initial stage, standing uncertainly to his position on the referee's count.
But the traditional red shorts of Arthur soon pressed ahead again. From the other corner, Rea - in opposing blue - was marked up quickly, noticeable damage developing under his orbital area as the fighters exchanged powerful shots.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, responded in kind with effective uppercuts as the pace hardly diminished over the full distance.
Arthur narrowly won the verdict with scoring tallies of even score, narrow lead and clearer margin, but each competitor were relentless and full of heart, everything their idol the legend embodied.
