UK light heavyweight Buatsi earned a win yet underwhelming debut to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a close ten-round contest at the Manchester venue.
But the challenger found success, delivering effective individual punches in a contest where the techniques failed to mesh, with excessive holding marring the contest.
Two judges scored it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my greatest performance but what defines champions? They succeed," the victor said in the arena as he was met by negative reactions from the audience.
The British fighter got back to winning after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers felt Parker, 31, merited the victory but the contender experienced the second defeat of his 28-bout career.
Buatsi Secures Victory in Slow Encounter
The fighter's advancement has slowed in the past few years through promotional disputes and considerable time of lack of fights.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to achieve expectations - possibly in what seems like a last chance - under new promotional backing.
He opened tentatively, with the two boxers prepared to overcommit in a tentative initial rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after damaging his hand mid-fight, was participating in his second bout at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to barely take the more effective periods.
The crowd's patience decreased during regular grabbing, with the challenger slipping to the canvas various instances during grappling.
The underdog closed well, but many rounds were difficult to score. However, ex-champion Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Hatton Tribute Fuels All-Manchester Battle
In the co-main event, Lyndon Arthur defeated Bradley Rea by close verdict in a terrific all-Manchester fight to capture the European light-heavyweight championship.
The stadium grew hushed for a extremely emotional memorial prior to the bout as ten bells sounded in memory of the city's native Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast match card in the location since Hatton's death. As the final chime disappeared, the silence transitioned to a chant of "there's only one Ricky Hatton".
The fighting inside the ropes reflected the feeling. The eventual winner was knocked down by a significant blow flush on the jaw in the second round, rising shakily to his position on the eight count.
But the Manchester United-red shorts of the fighter soon came forward again. On the opposite side, the opponent - in rival City blue - was damaged quickly, noticeable damage developing under his eye as the fighters traded powerful shots.
The challenger, 27, landed power punches but Arthur, 34, responded in kind with effective uppercuts as the pace hardly diminished over 12 rounds.
The victor barely secured the verdict with scoring tallies of draw, narrow lead and clearer margin, but both fighters were persistent and courageous, all the qualities their hero the legend stood for.
