British light-heavyweight Buatsi secured a victory yet disappointing debut to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a close 10-round fight at the Manchester venue.
But Parker found success, connecting with powerful clean blows in a match where the techniques failed to mesh, with frequent clinching spoiling the action.
The scoring judges had it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They prevail," Buatsi said in the arena as he was met by disapproval from the audience.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts believed Parker, thirty-one, should have been awarded the victory but the British boxer suffered the second loss of his 28-match career.
The Champion Secures Win in Slow Encounter
His career development has stalled in recent times through contract problems and long spells of lack of fights.
Previously predicted as the future of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what seems like a last chance - under fresh management.
He started carefully, with neither fighter ready to be aggressive in a calculated opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was participating in his second fight at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a protective stance to barely take the more effective periods.
The crowd's patience decreased during constant clinching, with the challenger slipping to the canvas various instances during clinches.
The underdog closed well, but multiple periods were difficult to score. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still seems difficult.
Hatton Homage Motivates Local Rivalry Battle
In the supporting bout, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific Manchester vs Manchester contest to win the European light heavyweight championship.
The venue grew hushed for a deeply poignant homage ahead of the contest as a bell ceremony tolled in memory of local hero Hatton, who died 46 years old in September.
It was the first major televised boxing event in the urban center since Hatton's death. As the last bell faded, the silence transitioned to a roar of "there's just one Ricky Hatton".
The fighting during the bout matched the emotion. The eventual winner was sent to the canvas by a left hook directly to the face in the second round, rising shakily to his position on the count of eight.
But the traditional red attire of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was damaged early, significant bruising developing under his orbital area as the pair traded hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor edged the verdict with scoring tallies of even score, 115-113 and 115-112, but each competitor were persistent and brave, all the qualities their inspiration the legend represented.
