UK light-heavyweight Buatsi earned a win yet underwhelming start to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a tight ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective individual punches in a contest where the techniques didn't complement each other, with excessive holding spoiling the fight.
The scoring judges had it 96-94 to the winner, with the final judge a even score.
"It wasn't my greatest display but what defines champions? They prevail," Buatsi commented in the ringside as he was greeted with disapproval from the audience.
The British fighter bounced back after his maiden career setback - an memorable fight with his previous opponent in last winter - to claim a twentieth professional win.
Several boxing experts felt Parker, thirty-one, deserved the win but the Derbyshire fighter endured the second loss of his 28-fight career.
The Champion Claims Victory in Uneventful Match
Buatsi's progress has slowed in recent times through management issues and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with the two boxers willing to be aggressive in a cagey early stages.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was participating in his second bout at the higher weight class.
By the halfway stage, the underdog had made it competitive, making life awkward for Buatsi, who utilized a solid defense to narrowly win the more effective periods.
The spectators' acceptance wore thin amid regular grabbing, with the challenger slipping to the canvas various instances during grappling.
Parker closed well, but many rounds were challenging to assess. However, former world champion the boxing analyst - commentating on Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the presence of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Fight
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding local rivalry battle to capture the European light heavyweight championship.
The arena grew hushed for a profoundly moving tribute before the fight as ten bells rang in memory of local hero Hatton, who died aged 46 in last month.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the concluding sound ended, the silence gave way to a shout of "there's just one Hatton".
The competition within the ring matched the feeling. The eventual winner was floored by a left hook directly to the face in the initial stage, getting up unsteadily to his feet on the eight count.
But the traditional red attire of the fighter soon pressed ahead again. Across the ring, Rea - in rival City blue - was damaged early, noticeable damage forming under his eye as the pair traded hard punches.
The challenger, 27, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the action seldom decreased over the full distance.
Arthur edged the decision with scoring tallies of even score, narrow lead and clearer margin, but both fighters were relentless and brave, exactly what their hero Hatton stood for.
