British light-heavyweight Buatsi secured a victory yet disappointing beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a close 10-round bout at the Co-op Live Arena.
But the challenger had his moments, delivering effective individual punches in a contest where the styles failed to mesh, with frequent clinching spoiling the action.
Two judges scored it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my best showing but what do champions do? They prevail," the victor said in the arena as he was greeted with disapproval from the spectators.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts felt the challenger, 31, should have been awarded the win but the British boxer suffered the second setback of his 28-bout career.
Buatsi Claims Triumph in Uneventful Encounter
His career development has slowed in recent times through promotional disputes and considerable time of inactivity.
Once tipped as the future of British boxing, he now stands trying to realize his potential - perhaps in what seems like a last chance - under recent support.
He started carefully, with neither fighter prepared to be aggressive in a cagey initial rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand during the bout, was making just his second bout at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for the favorite, who operated with a tight guard to barely take the better rounds.
The spectators' acceptance decreased amid regular grabbing, with Parker slipping to the canvas various instances during grappling.
The underdog finished the stronger, but many rounds were hard to judge. Although, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Memorial Inspires Manchester Derby Battle
In the supporting bout, Arthur defeated Rea by close verdict in a outstanding local rivalry contest to secure the European light heavyweight belt.
The arena grew hushed for a deeply poignant tribute prior to the bout as a bell ceremony tolled in honor of local hero Hatton, who died at age 46 in September.
It was the premier televised match card in the city since the passing of Hatton. As the final chime faded, the silence gave way to a shout of "there's only one Ricky Hatton".
The action inside the ropes matched the sentiment. The eventual winner was knocked down by a powerful punch flush on the face in the second round, standing uncertainly to his position on the referee's count.
But the red-colored attire of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was marked up soon, significant bruising forming under his orbital area as the fighters exchanged hard punches.
Rea, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action seldom decreased over twelve rounds.
The victor edged the result with scoring tallies of draw, 115-113 and 115-112, but both fighters were determined and brave, exactly what their hero the legend stood for.
