British light heavyweight Buatsi secured a victory yet disappointing start to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a competitive 10-round contest at the Manchester venue.
But Parker had his moments, connecting with powerful individual punches in a contest where the techniques didn't complement each other, with constant grabbing marring the fight.
Two judges scored it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest display but what defines champions? They prevail," the victor said in the ringside as he was faced negative reactions from the audience.
The Londoner bounced back after his maiden career setback - an epic battle 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 Derbyshire fighter suffered the second setback of his 28-bout professional journey.
The Champion Earns Win in Uneventful Encounter
His career development has stalled in recent years through contract problems and considerable time of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers ready to take risks in a cagey early stages.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for the favorite, who worked behind a tight guard to edge the better periods.
The crowd's patience wore thin during constant clinching, with the challenger slipping to the canvas various instances during close exchanges.
Parker closed well, but several stanzas were hard to judge. Although, former world champion Carl Frampton - working with Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Hatton Homage Inspires Manchester Derby Fight
In the co-main event, Arthur overcame Rea by split-decision in a excellent Manchester vs Manchester battle to capture the European light-heavyweight championship.
The venue became quiet for a profoundly moving memorial ahead of the contest as a bell ceremony sounded in remembrance of local hero Ricky Hatton, who succumbed 46 years old in last month.
It was the first major televised match card in the city since Hatton's death. As the last bell ended, the stillness transitioned to a shout of "only one Ricky Hatton".
The competition inside the ropes reflected the sentiment. Arthur was sent to the canvas by a significant blow directly to the chin in the initial stage, standing uncertainly to his feet on the referee's count.
But the red-colored equipment of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was marked up soon, heavy swelling developing under his eye as the duo exchanged punishing blows.
The challenger, 27, landed power punches but the champion, 34, matched the intensity with stinging uppercuts as the action seldom decreased over 12 rounds.
The victor edged the decision with scoring tallies of 114-114, narrow lead and 115-112, but each competitor were persistent and brave, exactly what their inspiration the legend stood for.
