UK light-heavyweight Buatsi secured a victory yet unimpressive debut to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a competitive ten-round bout at the boxing arena.
But the challenger had his moments, connecting with powerful individual punches in a fight where the techniques never quite clicked, with excessive holding spoiling the fight.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my greatest showing but how do champions respond? They succeed," the victor stated in the ringside as he was met by boos from the audience.
The British fighter returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Several boxing experts thought Parker, 31, deserved the win but the British boxer experienced the second loss of his 28-bout career.
Buatsi Claims Win in Uneventful Encounter
Buatsi's progress has stalled in recent times through promotional disputes and extended periods of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to realize his potential - perhaps in what appears to be a last chance - under recent support.
He opened tentatively, with the two boxers ready to take risks in a cagey opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after breaking his hand mid-fight, was making just his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for Buatsi, who operated with a protective stance to barely take the more effective stanzas.
The audience's tolerance diminished because of frequent holding, with Parker falling to the floor several times during close exchanges.
Parker ended stronger, but many rounds were hard to judge. Although, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the likes of power puncher Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Tribute Motivates Local Rivalry Contest
In the supporting bout, Arthur beat Bradley Rea by split-decision in a outstanding local rivalry battle to win the European light heavyweight championship.
The stadium fell silent for a extremely emotional homage before the fight as a bell ceremony sounded in remembrance of Manchester's own Hatton, who died aged 46 in recently.
It was the initial significant broadcast match card in the urban center since the passing of Hatton. As the final chime faded, the stillness transitioned to a roar of "there's just one Ricky Hatton".
The action inside the ropes equaled the sentiment. The eventual winner was sent to the canvas by a powerful punch flush on the jaw in the initial stage, rising shakily to his feet on the count of eight.
But the red-colored shorts of Arthur soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was damaged early, noticeable damage appearing under his face as the pair landed hard punches.
Rea, 27, delivered effective strikes but Arthur, 34, matched the intensity with effective uppercuts as the intensity rarely dropped over the full distance.
Arthur narrowly won the verdict with official scores of draw, close margin and clearer margin, but both fighters were persistent and brave, all the qualities their idol the legend embodied.
