British 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 bronze medallist's punch output likely gained him a majority decision in a tight 10-round contest at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a contest where the styles never quite clicked, with constant grabbing spoiling the contest.
The scoring judges had it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my finest display but how do champions respond? They succeed," Buatsi commented in the ringside as he was greeted with negative reactions from the audience.
The British fighter bounced back after his maiden career setback - an thrilling contest with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers thought Parker, thirty-one, merited the decision but the Derbyshire fighter experienced the second loss of his 28-fight career.
Buatsi Secures Win in Slow Encounter
Buatsi's progress has plateaued in recent years through contract problems and extended periods of lack of fights.
Previously predicted as the rising talent of British boxing, he now finds himself trying to realize his potential - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers prepared to overcommit in a cagey early stages.
Parker, whose single earlier setback came at the lower weight class against his former opponent in 2022 after breaking his hand during the bout, was participating in his second appearance at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a tight guard to edge the more effective rounds.
The audience's tolerance wore thin amid constant clinching, with Parker going down various instances during clinches.
Parker closed well, but multiple periods were challenging to assess. However, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - judging by this showing - still appears challenging.
Hatton Memorial Motivates All-Manchester Fight
In the secondary fight, Arthur overcame Bradley Rea by split-decision in a excellent all-Manchester battle to secure the European light heavyweight belt.
The stadium became quiet for a deeply poignant tribute ahead of the contest as ten bells sounded in memory of the city's native Hatton, who passed away 46 years old in recently.
It was the premier televised boxing event in the city since the passing of Hatton. As the final chime faded, the stillness gave way to a chant of "only one Ricky Hatton".
The competition within the ring reflected the feeling. Arthur was floored by a significant blow directly to the jaw in the initial stage, standing uncertainly to his feet on the referee's count.
But the traditional red shorts of the fighter soon came forward again. On the opposite side, Rea - in opposing blue - was marked up quickly, noticeable damage forming under his orbital area as the fighters traded punishing blows.
The challenger, 27, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace rarely dropped over twelve rounds.
Arthur barely secured the decision with judges scorecards of draw, close margin and wider gap, but both fighters were relentless and full of heart, all the qualities their hero Hatton represented.
