UK light-heavyweight Buatsi secured a victory yet unimpressive start to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a competitive ten-round fight at the boxing arena.
But Parker had his moments, landing some telling individual punches in a contest where the techniques failed to mesh, with constant grabbing disrupting the fight.
The officials scored it 96-94 in favor to the winner, with the third a even score.
"It wasn't my best display but what defines champions? They succeed," Buatsi commented in the arena as he was met by boos from the spectators.
The British fighter bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, should have been awarded the decision but the Derbyshire fighter endured the second defeat of his 28-fight professional journey.
The Champion Claims Victory in Slow Match
The fighter's advancement has stalled in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now is positioned trying to realize his potential - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers willing to be aggressive in a calculated 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 during the bout, was making just his second appearance at the higher weight class.
By the fight's midpoint, Parker had made it competitive, causing problems for the favorite, who utilized a solid defense to barely take the better stanzas.
The audience's tolerance decreased during frequent holding, with the challenger falling to the floor several times during close exchanges.
The underdog finished the stronger, but many rounds were hard to judge. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, awarding Buatsi just one round.
The victor advances, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Hatton Tribute Fuels All-Manchester Battle
In the secondary fight, Arthur defeated Bradley Rea by close verdict in a outstanding all-Manchester battle to secure the European light heavyweight championship.
The arena fell silent for a deeply poignant memorial ahead of the contest as a bell ceremony sounded in honor of the city's native Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the concluding sound ended, the quiet gave way to a shout of "there's only one Hatton".
The fighting within the ring reflected the feeling. The eventual winner was knocked down by a left hook flush on the face in the early round, standing uncertainly to his footing on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. Across the ring, the opponent - in competitive blue - was damaged early, heavy swelling developing under his eye as the pair exchanged hard punches.
Rea, twenty-seven, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the action rarely dropped over twelve rounds.
The victor barely secured the verdict with judges scorecards of draw, 115-113 and wider gap, but both fighters were relentless and courageous, all the qualities their hero the legend embodied.
