British light heavyweight Buatsi made a winning yet disappointing debut to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a competitive 10-round bout at the boxing arena.
But the challenger had his moments, connecting with powerful clean blows in a fight where the techniques failed to mesh, with excessive holding disrupting the action.
The officials scored it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my finest showing but what do champions do? They prevail," Buatsi stated in the arena as he was greeted with boos from the spectators.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to earn a twentieth professional win.
Several boxing experts thought Parker, 31, should have been awarded the victory but the contender endured the second loss of his 28-fight career.
Buatsi Secures Win in Dull Affair
Buatsi's progress has slowed in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to achieve expectations - possibly in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors ready to take risks in a tentative early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was competing in only his second appearance at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, causing problems for the favorite, who worked behind a protective stance to narrowly win the better stanzas.
The audience's tolerance decreased amid frequent holding, with the challenger falling to the floor multiple occasions during close exchanges.
The underdog closed well, but many rounds were difficult to score. Although, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of power puncher Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Memorial Motivates Local Rivalry Battle
In the supporting bout, Arthur overcame Rea by divided decision in a outstanding all-Manchester contest to capture the European light-heavyweight belt.
The stadium became quiet for a profoundly moving memorial ahead of the contest as 10 bells tolled in honor of the city's native Hatton, who passed away 46 years old in recently.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the concluding sound disappeared, the stillness gave way to a shout of "there's only one Hatton".
The action during the bout matched the sentiment. The eventual winner was knocked down by a left hook directly to the jaw in the second round, rising shakily to his position on the count of eight.
But the red-colored shorts of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was injured quickly, significant bruising forming under his face as the pair landed powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the action hardly diminished over twelve rounds.
Arthur edged the verdict with scoring tallies of even score, 115-113 and wider gap, but both fighters were relentless and brave, everything their inspiration the legend stood for.
