UK light heavyweight Buatsi earned a win yet disappointing debut to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a competitive 10-round bout at the Manchester venue.
But the challenger found success, landing some telling individual punches in a match where the styles failed to mesh, with excessive holding spoiling the fight.
The officials scored it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my best performance but what do champions do? They win," Buatsi commented in the ringside as he was faced boos from the crowd.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to earn a 20th career victory.
Various analysts believed the challenger, 31, deserved the win but the contender endured the second setback of his 28-match professional journey.
Buatsi Claims Win in Uneventful Affair
Buatsi's progress has stalled in recent times through management issues and long spells of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under recent support.
He started carefully, with the two boxers ready to overcommit in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against his former opponent in 2022 after damaging his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the middle rounds, Parker had made it competitive, creating difficulties for the favorite, who operated with a protective stance to barely take the better rounds.
The audience's tolerance wore thin because of frequent holding, with Parker going down multiple occasions during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. Although, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, giving Buatsi just one round.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Homage Motivates Local Rivalry Fight
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a outstanding local rivalry battle to win the European light-heavyweight championship.
The stadium became quiet for a deeply poignant memorial prior to the bout as 10 bells tolled in remembrance of Manchester's own Ricky Hatton, who died aged 46 in September.
It was the first major televised boxing event in the location since the passing of Hatton. As the final chime ended, the stillness became a roar of "there's just one Hatton".
The action during the bout reflected the emotion. The eventual winner was sent to the canvas by a left hook flush on the face in the second round, standing uncertainly to his feet on the eight count.
But the red-colored equipment of Arthur soon came forward again. On the opposite side, Rea - in competitive blue - was damaged early, significant bruising developing under his eye as the duo traded hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with effective uppercuts as the pace hardly diminished over 12 rounds.
Arthur edged the verdict with official scores of even score, 115-113 and clearer margin, but both fighters were persistent and brave, exactly what their hero the legend represented.
