British light heavyweight Buatsi made a winning yet disappointing start to his career under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger found success, delivering effective individual punches in a fight where the techniques failed to mesh, with constant grabbing marring the fight.
Two judges scored it 96-94 to the winner, with the third a even score.
"It wasn't my finest showing but how do champions respond? They succeed," Buatsi stated in the arena as he was greeted with disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Several boxing experts believed Parker, thirty-one, should have been awarded the decision but the British boxer suffered the second defeat of his 28-fight professional journey.
Buatsi Claims Win in Uneventful Affair
His career development has slowed in recent times through contract problems and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with the two boxers ready to be aggressive in a tentative early stages.
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 making just his second fight at the higher weight class.
By the halfway stage, the underdog had made it competitive, creating difficulties for the favorite, who worked behind a protective stance to edge the more effective stanzas.
The audience's tolerance diminished because of regular grabbing, with Parker falling to the floor various instances during clinches.
The underdog ended stronger, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just a single round.
The victor moves on, but with the presence of power puncher Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Inspires Local Rivalry Fight
In the secondary fight, Lyndon Arthur beat Rea by split-decision in a outstanding all-Manchester battle to capture the European light heavyweight belt.
The arena became quiet for a deeply poignant homage prior to the bout as a bell ceremony sounded in memory of the city's native Hatton, who died 46 years old in recently.
It was the premier televised fight night in the city since Hatton's death. As the last bell ended, the silence transitioned to a chant of "there's only one Ricky Hatton".
The fighting during the bout equaled the emotion. The eventual winner was knocked down by a left hook squarely on the face in the initial stage, getting up unsteadily to his footing on the eight count.
But the red-colored shorts of the fighter soon pressed ahead again. From the other corner, the opponent - in rival City blue - was injured quickly, noticeable damage developing under his orbital area as the fighters traded hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace seldom decreased over 12 rounds.
Arthur edged the decision with scoring tallies of draw, 115-113 and 115-112, but each competitor were persistent and courageous, exactly what their hero the legend embodied.
