UK light-heavyweight Buatsi earned a win yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a competitive ten-round fight at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling clean blows in a fight where the techniques never quite clicked, with frequent clinching disrupting the action.
The scoring judges scored it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest display but what do champions do? They prevail," the victor commented in the ringside as he was faced disapproval from the spectators.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a twentieth professional win.
Various analysts thought Parker, thirty-one, should have been awarded the victory but the British boxer suffered the second loss of his 28-match professional journey.
Buatsi Earns Win in Dull Encounter
Buatsi's progress has slowed in recent years through promotional disputes and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now is positioned trying to realize his potential - maybe in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with neither fighter willing to overcommit in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second fight at light heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to edge the more effective periods.
The spectators' acceptance wore thin because of frequent holding, with Parker slipping to the canvas several times during clinches.
Parker ended stronger, but multiple periods were difficult to score. Although, former world champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Hatton Memorial Motivates Local Rivalry Fight
In the secondary fight, Lyndon Arthur defeated Rea by close verdict in a outstanding Manchester vs Manchester fight to win the European light heavyweight belt.
The stadium fell silent for a extremely emotional homage before the fight as 10 bells sounded in honor of local hero Ricky Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the last bell disappeared, the stillness gave way to a chant of "there's only one Ricky Hatton".
The fighting inside the ropes matched the feeling. Arthur was sent to the canvas by a powerful punch directly to the chin in the second round, getting up unsteadily to his position on the count of eight.
But the red-colored attire of Arthur soon pressed ahead again. From the other corner, the opponent - in rival City blue - was marked up quickly, heavy swelling forming under his eye as the fighters exchanged hard punches.
The challenger, twenty-seven, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the intensity hardly diminished over twelve rounds.
Arthur edged the result with judges scorecards of 114-114, 115-113 and wider gap, but both fighters were persistent and brave, everything their idol the legend embodied.
