British light heavyweight Buatsi secured a victory yet unimpressive debut to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a competitive 10-round contest at the boxing arena.
But the challenger landed significant shots, connecting with powerful individual punches in a contest where the styles failed to mesh, with frequent clinching spoiling the fight.
The officials judged it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my best showing but what do champions do? They win," the victor commented in the ring as he was met by disapproval from the audience.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts thought Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter suffered the second loss of his 28-bout career.
The Champion Secures Win in Uneventful Encounter
His career development has plateaued in the past few years through contract problems and considerable time of lack of fights.
Once tipped as the rising talent of UK boxing, he now stands trying to realize his potential - perhaps in what feels like a last chance - under new promotional backing.
He began cautiously, with neither fighter prepared to be aggressive in a calculated opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after suffering a hand injury in the contest, was competing in only his second appearance at the higher weight class.
By the middle rounds, Parker had made it competitive, 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 regular grabbing, with Parker falling to the floor various instances during clinches.
The underdog closed well, but multiple periods were hard to judge. Although, previous titleholder the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, awarding Buatsi just one round.
Buatsi advances, but with the likes of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Tribute Inspires All-Manchester Fight
In the co-main event, Arthur defeated Bradley Rea by divided decision in a outstanding local rivalry contest to secure the European light heavyweight belt.
The stadium became quiet for a deeply poignant homage prior to the bout as a bell ceremony tolled in honor of Manchester's own Hatton, who passed away aged 46 in last month.
It was the premier televised boxing event in the city since the passing of Hatton. As the concluding sound ended, the silence gave way to a roar of "only one Ricky Hatton".
The action inside the ropes equaled the sentiment. The eventual winner was knocked down by a left hook flush on the face in the second round, getting up unsteadily to his footing on the count of eight.
But the red-colored shorts of Arthur soon came forward again. From the other corner, the opponent - in competitive blue - was injured early, significant bruising developing under his orbital area as the duo traded powerful shots.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor narrowly won the decision with judges scorecards of 114-114, close margin and clearer margin, but both fighters were persistent and brave, exactly what their inspiration the legend represented.
