UK light-heavyweight Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a majority decision in a tight 10-round bout at the boxing arena.
But Parker had his moments, connecting with powerful clean blows in a match where the techniques failed to mesh, with constant grabbing marring the fight.
The officials had it 96-94 to the winner, with the third a even score.
"It wasn't my finest display but what do champions do? They win," Buatsi stated in the ringside as he was faced negative reactions from the spectators.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to claim a 20th career victory.
Several boxing experts felt Parker, 31, should have been awarded the decision but the Derbyshire fighter experienced the second loss of his 28-bout professional journey.
The Champion Secures Win in Slow Match
Buatsi's progress has stalled in recent years through contract problems and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now stands trying to achieve expectations - maybe in what feels like a ultimate opportunity - under recent support.
He started carefully, with neither fighter ready to be aggressive in a tentative initial rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who worked behind a solid defense to narrowly win the cleaner rounds.
The audience's tolerance diminished because of constant clinching, with Parker going down multiple occasions during clinches.
The underdog ended stronger, but multiple periods were hard to judge. Although, previous titleholder the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the likes of heavy hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Hatton Tribute Inspires Local Rivalry Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by split-decision in a outstanding Manchester vs Manchester contest to win the European light heavyweight title.
The stadium grew hushed for a profoundly moving tribute ahead of the contest as ten bells rang in memory of local hero Hatton, who died aged 46 in last month.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the final chime disappeared, the stillness transitioned to a shout of "there's only one Hatton".
The action inside the ropes matched the feeling. The eventual winner was floored by a powerful punch flush on the jaw in the early round, getting up unsteadily to his position on the eight count.
But the Manchester United-red attire of Arthur soon advanced again. On the opposite side, the opponent - in rival City blue - was injured early, significant bruising appearing under his orbital area as the fighters traded punishing blows.
Rea, twenty-seven, landed power punches but the champion, 34, responded in kind with stinging uppercuts as the intensity hardly diminished over 12 rounds.
The victor barely secured the verdict with scoring tallies of even score, narrow lead and 115-112, but the two athletes were determined and full of heart, all the qualities their hero the legend stood for.
