UK light heavyweight Buatsi earned a win yet underwhelming start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a close ten-round fight at the Co-op Live Arena.
But Parker landed significant shots, landing some telling single shots in a fight where the styles failed to mesh, with constant grabbing marring the action.
The officials judged it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my best display but what do champions do? They win," the victor said in the arena as he was greeted with disapproval from the audience.
The British fighter got back to winning after his first professional defeat - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, merited the win but the Derbyshire fighter suffered the second defeat of his 28-fight career.
The Champion Claims Triumph in Dull Affair
His career development has plateaued in recent times through management issues and long spells of inactivity.
Once tipped as the next star of UK boxing, he now stands trying to achieve expectations - possibly in what seems like a final roll of the dice - under recent support.
He began cautiously, with neither fighter willing to be aggressive in a calculated early stages.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was making just his second bout at light-heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who operated with a protective stance to narrowly win the more effective rounds.
The audience's tolerance decreased amid frequent holding, with Parker falling to the floor several times during close exchanges.
Parker closed well, but several stanzas were challenging to assess. Nevertheless, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Hatton Memorial Motivates All-Manchester Fight
In the co-main event, Arthur overcame Bradley Rea by close verdict in a terrific Manchester vs Manchester battle to secure the European light heavyweight championship.
The arena grew hushed for a extremely emotional memorial ahead of the contest as 10 bells rang in memory of local hero Ricky Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the concluding sound ended, the stillness gave way to a shout of "only one Ricky Hatton".
The action inside the ropes equaled the emotion. Arthur was floored by a significant blow directly to the jaw in the early round, standing uncertainly to his feet on the count of eight.
But the red-colored attire of the fighter soon came forward again. Across the ring, the opponent - in rival City blue - was marked up quickly, heavy swelling developing under his eye as the fighters landed powerful shots.
The challenger, 27, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the intensity hardly diminished over 12 rounds.
Arthur barely secured the verdict with judges scorecards of draw, 115-113 and 115-112, but the two athletes were relentless and full of heart, everything their hero Hatton embodied.
