British light heavyweight Buatsi secured a victory yet unimpressive beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a majority decision in a close 10-round bout at the boxing arena.
But the challenger had his moments, delivering effective individual punches in a fight where the styles failed to mesh, with constant grabbing spoiling the fight.
Two judges scored it 96-94 for to the winner, with the third a even score.
"It wasn't my greatest display but how do champions respond? They prevail," Buatsi said in the arena as he was met by disapproval from the audience.
The Londoner returned to winning ways after his first professional defeat - an epic battle with Callum Smith in February - to claim a 20th pro success.
Various analysts felt Parker, thirty-one, should have been awarded the win but the contender experienced the second defeat of his 28-bout career.
Buatsi Secures Victory in Dull Encounter
His career development has slowed in the past few years through management issues and long spells of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to realize his potential - maybe in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with the two boxers ready to take risks in a calculated early stages.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after damaging his hand in the contest, was participating in his second bout at the higher weight class.
By the middle rounds, Parker had kept it close, making life awkward for the favorite, who operated with a tight guard to narrowly win the better stanzas.
The spectators' acceptance decreased because of constant clinching, with the challenger going down several times during close exchanges.
The underdog ended stronger, but many rounds were difficult to score. Nevertheless, former world champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Ricky Hatton Memorial Motivates Manchester Derby Battle
In the supporting bout, Lyndon Arthur defeated Rea by split-decision in a terrific Manchester vs Manchester fight to capture the European light heavyweight championship.
The venue grew hushed for a profoundly moving tribute prior to the bout as ten bells tolled in honor of the city's native Hatton, who passed away 46 years old in September.
It was the first major televised match card in the location since Hatton's passing. As the concluding sound disappeared, the stillness became a shout of "only one Ricky Hatton".
The competition within the ring reflected the feeling. Arthur was knocked down by a left hook squarely on the face in the initial stage, rising shakily to his footing on the eight count.
But the traditional red attire of the fighter soon advanced again. On the opposite side, the opponent - in rival City blue - was marked up early, heavy swelling forming under his face as the pair exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the intensity seldom decreased over twelve rounds.
The victor barely secured the result with scoring tallies of even score, close margin and 115-112, but each competitor were persistent and full of heart, everything their hero the legend embodied.
