UK light heavyweight Buatsi secured a victory yet unimpressive debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a split decision in a competitive ten-round fight at the Manchester venue.
But Parker had his moments, connecting with powerful clean blows in a match where the approaches failed to mesh, with frequent clinching disrupting the fight.
The scoring judges judged it 96-94 to the winner, with the remaining official a even score.
"It wasn't my best display but what do champions do? They prevail," the victor said in the ring as he was met by boos from the audience.
The Londoner bounced back after his initial pro loss - an epic battle with Callum Smith in February - to earn a twentieth professional win.
Some ringside observers felt Parker, 31, deserved the win but the Derbyshire fighter suffered the second loss of his 28-match professional journey.
Buatsi Claims Win in Uneventful Encounter
His career development has slowed in recent years through promotional disputes and long spells of lack of fights.
Earlier forecast as the rising talent of the British fight scene, he now is positioned trying to realize his potential - perhaps in what feels like a final roll of the dice - under recent support.
He opened tentatively, with neither fighter prepared to overcommit in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand during the bout, was competing in only his second bout at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for the favorite, who operated with a solid defense to narrowly win the more effective stanzas.
The crowd's patience decreased because of frequent holding, with Parker going down multiple occasions during close exchanges.
Parker finished the stronger, but multiple periods were difficult to score. Nevertheless, former world champion the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Hatton Homage Fuels All-Manchester Battle
In the co-main event, Arthur defeated Bradley Rea by split-decision in a terrific Manchester vs Manchester contest to capture the European light-heavyweight championship.
The stadium fell silent for a profoundly moving tribute prior to the bout as ten bells tolled in remembrance of local hero Ricky Hatton, who succumbed at age 46 in recently.
It was the first major televised fight night in the city since the passing of Hatton. As the last bell disappeared, the quiet transitioned to a chant of "there's only one Ricky Hatton".
The fighting during the bout equaled the emotion. The eventual winner was knocked down by a left hook flush on the jaw in the second round, getting up unsteadily to his footing on the eight count.
But the Manchester United-red equipment of Arthur soon came forward again. From the other corner, Rea - in opposing blue - was damaged early, heavy swelling appearing under his eye as the fighters traded powerful shots.
Rea, 27, landed power punches but the champion, 34, responded in kind with powerful upward punches as the action hardly diminished over twelve rounds.
Arthur edged the decision with scoring tallies of even score, 115-113 and wider gap, but both fighters were relentless and full of heart, all the qualities their idol Hatton stood for.
