British light heavyweight Buatsi made a winning yet underwhelming debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a competitive 10-round bout at the Co-op Live Arena.
But the challenger found success, landing some telling clean blows in a match where the approaches didn't complement each other, with excessive holding spoiling the fight.
The officials judged it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my greatest display but how do champions respond? They prevail," the victor stated in the ringside as he was met by boos from the spectators.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in last winter - to secure a 20th career victory.
Several boxing experts believed the challenger, thirty-one, deserved the decision but the Derbyshire fighter experienced the second setback of his 28-bout professional journey.
Buatsi Secures Victory in Uneventful Encounter
The fighter's advancement has stalled in recent times through contract problems and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under recent support.
He started carefully, with the two boxers willing to take risks in a calculated early stages.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was participating in his second appearance at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for Buatsi, who worked behind a tight guard to narrowly win the better rounds.
The crowd's patience wore thin because of frequent holding, with the challenger falling to the floor various instances during clinches.
Parker ended stronger, but several stanzas were difficult to score. Although, ex-champion the boxing analyst - commentating on Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the caliber of hard hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Contest
In the secondary fight, Arthur overcame Bradley Rea by close verdict in a terrific all-Manchester battle to secure the European light-heavyweight championship.
The stadium grew hushed for a profoundly moving memorial before the fight as 10 bells rang in remembrance of local hero Ricky Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the final chime ended, the quiet gave way to a shout of "there's only one Ricky Hatton".
The action during the bout equaled the emotion. The eventual winner was floored by a significant blow directly to the jaw in the initial stage, rising shakily to his feet on the referee's count.
But the red-colored equipment of the fighter soon advanced again. From the other corner, Rea - in opposing blue - was damaged early, heavy swelling appearing under his eye as the duo traded punishing blows.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the intensity hardly diminished over 12 rounds.
Arthur edged the verdict with scoring tallies of 114-114, close margin and 115-112, but the two athletes were relentless and courageous, everything their inspiration Hatton stood for.
