UK light-heavyweight Buatsi secured a victory yet disappointing beginning to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a tight ten-round fight at the Co-op Live Arena.
But Parker had his moments, delivering effective individual punches in a fight where the approaches didn't complement each other, with frequent clinching spoiling the contest.
The scoring judges had it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my best performance but what do champions do? They prevail," Buatsi said in the arena as he was greeted with negative reactions from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in February - to secure a 20th career victory.
Various analysts believed Parker, 31, should have been awarded the decision but the British boxer experienced the second defeat of his 28-fight professional journey.
Buatsi Claims Triumph in Slow Match
His career development has plateaued in recent times through promotional disputes and extended periods of lack of fights.
Once tipped as the next star of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what feels like a last chance - under new promotional backing.
He started carefully, with the two boxers prepared to overcommit in a calculated early stages.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after damaging his hand in the contest, was participating in his second appearance at light-heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for the favorite, who utilized a protective stance to barely take the better periods.
The audience's tolerance diminished during regular grabbing, with the challenger falling to the floor several times during grappling.
The underdog ended stronger, but many rounds were difficult to score. However, former world champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, giving Buatsi just a single round.
The victor moves on, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Hatton Tribute Fuels All-Manchester Battle
In the secondary fight, Arthur defeated Rea by divided decision in a excellent all-Manchester contest to win the European light-heavyweight championship.
The stadium fell silent for a deeply poignant memorial prior to the bout as 10 bells rang in memory of local hero Hatton, who passed away aged 46 in September.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the concluding sound disappeared, the stillness gave way to a shout of "only one Ricky Hatton".
The fighting inside the ropes equaled the emotion. Arthur was knocked down by a powerful punch flush on the jaw in the initial stage, rising shakily to his position on the count of eight.
But the red-colored equipment of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was damaged early, heavy swelling developing under his face as the pair landed punishing blows.
The challenger, 27, connected with strong blows but Arthur, thirty-four, fought fire with fire with powerful upward punches as the pace seldom decreased over twelve rounds.
The victor narrowly won the decision with official scores of 114-114, narrow lead and clearer margin, but each competitor were determined and full of heart, everything their inspiration Hatton represented.
