UK light-heavyweight Buatsi made a winning yet underwhelming beginning to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a majority decision in a competitive ten-round bout at the Co-op Live Arena.
But the challenger had his moments, landing some telling single shots in a contest where the styles didn't complement each other, with constant grabbing disrupting the fight.
Two judges had it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my greatest showing but what defines champions? They succeed," the victor said in the ringside as he was met by boos from the crowd.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Several boxing experts felt the challenger, 31, merited the decision but the British boxer experienced the second loss of his 28-fight professional journey.
Buatsi Secures Win in Uneventful Affair
His career development has stalled in recent times through promotional disputes and long spells of lack of fights.
Previously predicted as the rising talent of British boxing, he now finds himself trying to realize his potential - maybe in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with neither fighter ready to take risks in a cagey early stages.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was participating in his second fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for the favorite, who utilized a tight guard to barely take the better stanzas.
The spectators' acceptance wore thin during frequent holding, with the challenger going down various instances during grappling.
The underdog ended stronger, but multiple periods were difficult to score. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor progresses, but with the caliber of power puncher David Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Hatton Tribute Motivates Manchester Derby Fight
In the secondary fight, Arthur defeated Rea by split-decision in a terrific Manchester vs Manchester battle to capture the European light-heavyweight championship.
The arena fell silent for a extremely emotional memorial before the fight as ten bells tolled in remembrance of the city's native Hatton, who died 46 years old in last month.
It was the first major televised fight night in the city since Hatton's death. As the final chime disappeared, the silence gave way to a chant of "there's only one Hatton".
The competition within the ring equaled the emotion. Arthur was floored by a left hook squarely on the chin in the initial stage, standing uncertainly to his footing on the count of eight.
But the Manchester United-red attire of the fighter soon came forward again. On the opposite side, the opponent - in competitive blue - was marked up early, significant bruising developing under his eye as the duo traded hard punches.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the pace rarely dropped over 12 rounds.
Arthur edged the verdict with scoring tallies of draw, 115-113 and clearer margin, but each competitor were determined and courageous, everything their hero the legend embodied.
