UK light heavyweight Buatsi secured a victory yet underwhelming start to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But Parker found success, connecting with powerful individual punches in a match where the styles never quite clicked, with excessive holding spoiling the action.
The officials scored it 96-94 to the winner, with the remaining official a even score.
"It wasn't my finest display but how do champions respond? They succeed," Buatsi stated in the ringside as he was met by boos from the crowd.
The British fighter returned to winning ways after his first professional defeat - an epic battle with his previous opponent in last winter - to secure a 20th pro success.
Several boxing experts felt Parker, thirty-one, should have been awarded the decision but the contender endured the second setback of his 28-fight professional journey.
The Champion Earns Victory in Slow Match
His career development has slowed in the past few years through management issues and long spells of lack of fights.
Earlier forecast as the rising talent of the British fight scene, he now stands trying to fulfil that early promise - possibly in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors ready to take risks in a tentative opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at light heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to narrowly win the cleaner periods.
The crowd's patience wore thin during regular grabbing, with the challenger going down several times during clinches.
Parker ended stronger, but multiple periods were difficult to score. Although, former world champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just one round.
Buatsi moves on, but with the presence of hard hitter David Benavidez, and Russian star Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Tribute Inspires All-Manchester Fight
In the secondary fight, Arthur beat Rea by close verdict in a excellent all-Manchester contest to secure the European light-heavyweight title.
The stadium grew hushed for a deeply poignant tribute prior to the bout as a bell ceremony tolled in honor of local hero Ricky Hatton, who died 46 years old in last month.
It was the initial significant broadcast match card in the location since Hatton's death. As the final chime ended, the silence gave way to a chant of "there's only one Hatton".
The action inside the ropes reflected the feeling. The eventual winner was sent to the canvas by a significant blow flush on the face in the early round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon advanced again. From the other corner, the opponent - in opposing blue - was marked up early, significant bruising forming under his eye as the duo landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with powerful upward punches as the action seldom decreased over the full distance.
Arthur edged the decision with scoring tallies of draw, close margin and wider gap, but both fighters were relentless and brave, everything their inspiration the legend stood for.
