UK light-heavyweight Buatsi earned a win yet disappointing beginning to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a close ten-round fight at the Co-op Live Arena.
But Parker found success, landing some telling clean blows in a contest where the approaches never quite clicked, with frequent clinching spoiling the contest.
The officials had it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my finest performance but what defines champions? They prevail," the victor commented in the arena as he was greeted with boos from the spectators.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in last winter - to claim a 20th pro success.
Some ringside observers felt Parker, thirty-one, deserved the decision but the Derbyshire fighter experienced the second defeat of his 28-bout career.
Buatsi Claims Victory in Dull Encounter
The fighter's advancement has plateaued in the past few years through promotional disputes and considerable time of lack of fights.
Once tipped as the next star of UK boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with both competitors ready to take risks in a calculated opening few rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was competing in only his second fight at light-heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for Buatsi, who operated with a protective stance to barely take the better rounds.
The spectators' acceptance decreased during regular grabbing, with Parker going down multiple occasions during clinches.
The underdog finished the stronger, but many rounds were challenging to assess. However, former world champion Carl Frampton - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Motivates All-Manchester Contest
In the secondary fight, Lyndon Arthur beat Rea by close verdict in a excellent Manchester vs Manchester battle to win the continental belt.
The stadium became quiet for a profoundly moving homage before the fight as ten bells tolled in memory of the city's native Ricky Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the final chime faded, the quiet gave way to a shout of "there's just one Hatton".
The competition inside the ropes equaled the feeling. The eventual winner was sent to the canvas by a powerful punch flush on the jaw in the initial stage, getting up unsteadily to his position on the count of eight.
But the Manchester United-red equipment of Arthur soon came forward again. From the other corner, the opponent - in rival City blue - was injured quickly, noticeable damage developing under his eye as the duo traded powerful shots.
The challenger, 27, connected with strong blows but the champion, 34, fought fire with fire with stinging uppercuts as the action seldom decreased over 12 rounds.
Arthur barely secured the decision with scoring tallies of even score, close margin and clearer margin, but both fighters were determined and courageous, all the qualities their inspiration the legend embodied.
