British light heavyweight Buatsi secured a victory yet underwhelming beginning to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a close ten-round contest at the boxing arena.
But the challenger found success, connecting with powerful single shots in a fight where the approaches never quite clicked, with excessive holding marring the action.
The scoring judges scored it 96-94 to Buatsi, with the final judge a 95-95.
"It wasn't my best showing but what do champions do? They succeed," the victor commented in the arena as he was met by negative reactions from the audience.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to earn a 20th pro success.
Some ringside observers thought the challenger, thirty-one, should have been awarded the win but the Derbyshire fighter suffered the second defeat of his 28-bout career.
Buatsi Earns Victory in Uneventful Encounter
The fighter's advancement has plateaued in recent years through management issues and extended periods of inactivity.
Earlier forecast as the next star of British boxing, he now finds himself trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with both competitors willing to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was competing in only his second fight at the higher weight class.
By the middle rounds, Parker had stayed in contention, causing problems for Buatsi, who worked behind a protective stance to barely take the cleaner periods.
The spectators' acceptance decreased because of regular grabbing, with the challenger slipping to the canvas several times during close exchanges.
The underdog closed well, but several stanzas were difficult to score. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi moves on, but with the presence of power puncher David Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Memorial Inspires Manchester Derby Contest
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a excellent Manchester vs Manchester fight to secure the European light heavyweight title.
The stadium fell silent for a deeply poignant tribute before the fight as 10 bells rang in honor of local hero Hatton, who died 46 years old in last month.
It was the first major televised boxing event in the city since the passing of Hatton. As the last bell ended, the silence became a chant of "there's only one Ricky Hatton".
The fighting inside the ropes reflected the feeling. The eventual winner was floored by a left hook directly to the jaw in the early round, getting up unsteadily to his footing on the eight count.
But the red-colored shorts of the fighter soon pressed ahead again. From the other corner, the opponent - in competitive blue - was damaged soon, heavy swelling developing under his eye as the pair traded punishing blows.
Rea, 27, landed power punches but Arthur, thirty-four, matched the intensity with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur barely secured the result with scoring tallies of draw, close margin and 115-112, but both fighters were determined and full of heart, all the qualities their inspiration the legend represented.
