British light-heavyweight Buatsi made a winning yet unimpressive debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a split decision in a close 10-round fight at the Manchester venue.
But the challenger found success, connecting with powerful single shots in a contest where the techniques failed to mesh, with constant grabbing disrupting the action.
Two judges judged it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest performance but what do champions do? They prevail," the victor said in the ringside as he was faced boos from the crowd.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in February - to earn a 20th pro success.
Some ringside observers felt Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter endured the second loss of his 28-match career.
Buatsi Claims Triumph in Uneventful Encounter
Buatsi's progress has plateaued in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the rising talent of British boxing, he now stands trying to achieve expectations - maybe in what feels like a ultimate opportunity - under recent support.
He opened tentatively, with both competitors willing to be aggressive in a cagey early stages.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after breaking his hand in the contest, was participating in his second bout at light heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who utilized a solid defense to barely take the cleaner stanzas.
The spectators' acceptance diminished because of regular grabbing, with Parker falling to the floor multiple occasions during close exchanges.
The underdog ended stronger, but several stanzas were challenging to assess. However, former world champion the boxing analyst - working with the broadcast network - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Homage Inspires All-Manchester Contest
In the secondary fight, Arthur defeated Rea by close verdict in a excellent local rivalry battle to capture the European light heavyweight belt.
The stadium became quiet for a extremely emotional memorial ahead of the contest as a bell ceremony tolled in memory of the city's native Ricky Hatton, who passed away aged 46 in September.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the final chime disappeared, the stillness became a chant of "there's only one Ricky Hatton".
The fighting within the ring matched the sentiment. Arthur was sent to the canvas by a left hook squarely on the jaw in the initial stage, rising shakily to his position on the eight count.
But the red-colored equipment of Arthur soon pressed ahead again. From the other corner, Rea - in competitive blue - was damaged soon, significant bruising forming under his orbital area as the fighters traded powerful shots.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with stinging uppercuts as the pace rarely dropped over twelve rounds.
Arthur barely secured the decision with scoring tallies of 114-114, narrow lead and 115-112, but both fighters were relentless and courageous, everything their hero Hatton embodied.
