UK light heavyweight Buatsi made a winning yet unimpressive debut to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive 10-round fight at the Manchester venue.
But Parker had his moments, landing some telling individual punches in a fight where the techniques failed to mesh, with excessive holding disrupting the contest.
The scoring judges judged it 96-94 for to the winner, with the final judge a even score.
"It wasn't my finest showing but what defines champions? They prevail," Buatsi said in the ringside as he was met by disapproval from the spectators.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a 20th pro success.
Several boxing experts thought Parker, thirty-one, merited the decision but the British boxer endured the second setback of his 28-match career.
Buatsi Claims Triumph in Dull Match
The fighter's advancement has stalled in recent times through management issues and extended periods of inactivity.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under recent support.
He started carefully, with neither fighter ready to be aggressive in a cagey early stages.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was making just his second fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for the favorite, who worked behind a protective stance to barely take the cleaner rounds.
The crowd's patience decreased amid regular grabbing, with the challenger falling to the floor various instances during clinches.
The underdog finished the stronger, but many rounds were challenging to assess. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor advances, but with the presence of heavy hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Homage Motivates Manchester Derby Battle
In the supporting bout, Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester contest to win the continental belt.
The stadium fell silent for a deeply poignant homage ahead of the contest as 10 bells rang in remembrance of local hero Ricky Hatton, who died at age 46 in September.
It was the first major televised boxing event in the location since Hatton's passing. As the final chime ended, the stillness transitioned to a chant of "only one Hatton".
The competition during the bout matched the emotion. The eventual winner was knocked down by a powerful punch directly to the jaw in the second round, rising shakily to his footing on the count of eight.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, Rea - in opposing blue - was damaged soon, noticeable damage appearing under his eye as the pair landed powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with powerful upward punches as the pace hardly diminished over 12 rounds.
The victor narrowly won the result with judges scorecards of draw, close margin and clearer margin, but both fighters were relentless and courageous, all the qualities their idol the legend embodied.
