UK light-heavyweight Buatsi made a winning yet underwhelming debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a tight 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling individual punches in a fight where the approaches didn't complement each other, with constant grabbing marring the fight.
Two judges scored it 96-94 for to the winner, with the third a even score.
"It wasn't my best showing but how do champions respond? They win," the victor said in the ringside as he was met by negative reactions from the crowd.
The Londoner bounced back after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Some ringside observers believed the challenger, 31, should have been awarded the victory but the Derbyshire fighter suffered the second loss of his 28-match professional journey.
Buatsi Secures Victory in Slow Affair
Buatsi's progress has stalled in recent times through management issues and long spells of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a last chance - under recent support.
He began cautiously, with both competitors willing to take risks in a cagey opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was participating in his second fight at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who utilized a protective stance to edge the better stanzas.
The spectators' acceptance decreased during frequent holding, with Parker falling to the floor multiple occasions during clinches.
Parker closed well, but many rounds were hard to judge. Nevertheless, former world champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Fuels Local Rivalry Contest
In the secondary fight, Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester fight to capture the continental title.
The arena fell silent for a extremely emotional homage ahead of the contest as ten bells rang in memory of the city's native Ricky Hatton, who succumbed at age 46 in recently.
It was the first major televised fight night in the location since Hatton's death. As the final chime ended, the stillness transitioned to a roar of "there's only one Ricky Hatton".
The competition inside the ropes equaled the sentiment. The eventual winner was floored by a left hook squarely on the chin in the initial stage, getting up unsteadily to his feet on the count of eight.
But the red-colored attire of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was marked up early, heavy swelling developing under his face as the duo traded punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over twelve rounds.
The victor narrowly won the decision with scoring tallies of draw, narrow lead and clearer margin, but both fighters were relentless and courageous, everything their hero the legend stood for.
