UK light-heavyweight Buatsi secured a victory yet underwhelming start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a fight where the techniques didn't complement each other, with constant grabbing disrupting the fight.
The scoring judges had it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest display but how do champions respond? They prevail," the victor commented in the arena as he was met by negative reactions from the crowd.
The Londoner bounced back after his first professional defeat - an epic battle with Callum Smith in last winter - to claim a 20th pro success.
Several boxing experts thought Parker, thirty-one, should have been awarded the win but the contender experienced the second loss of his 28-match professional journey.
Buatsi Earns Victory in Slow Encounter
The fighter's advancement has plateaued in recent times through promotional disputes and long spells of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to achieve expectations - maybe in what seems like a last chance - under recent support.
He began cautiously, with the two boxers ready to overcommit in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after damaging his hand in the contest, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a solid defense to narrowly win the better rounds.
The crowd's patience diminished amid frequent holding, with the challenger falling to the floor several times during clinches.
The underdog ended stronger, but many rounds were difficult to score. Although, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the presence of hard hitter David Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Memorial Motivates Manchester Derby Fight
In the supporting bout, Arthur defeated Bradley Rea by close verdict in a excellent Manchester vs Manchester contest to win the continental title.
The arena fell silent for a profoundly moving homage prior to the bout as 10 bells rang in honor of Manchester's own Ricky Hatton, who succumbed 46 years old in last month.
It was the premier televised match card in the location since Hatton's death. As the concluding sound ended, the quiet gave way to a roar of "only one Hatton".
The action inside the ropes matched the emotion. Arthur was sent to the canvas by a significant blow flush on the face in the initial stage, standing uncertainly to his feet on the eight count.
But the Manchester United-red attire of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was injured soon, noticeable damage forming under his eye as the duo landed punishing blows.
The challenger, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over 12 rounds.
Arthur barely secured the result with scoring tallies of draw, close margin and wider gap, but both fighters were determined and courageous, exactly what their hero the legend embodied.
