UK light-heavyweight Buatsi made a winning yet unimpressive debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a competitive 10-round fight at the boxing arena.
But the challenger had his moments, landing some telling individual punches in a contest where the approaches never quite clicked, with excessive holding disrupting the fight.
The scoring judges scored it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They prevail," the victor stated in the arena as he was met by negative reactions from the audience.
The Londoner bounced back after his initial pro loss - an memorable fight with his previous opponent in February - to secure a 20th pro success.
Various analysts thought the challenger, thirty-one, should have been awarded the win but the British boxer suffered the second defeat of his 28-fight professional journey.
The fighter's advancement has slowed in the past few years through promotional disputes and considerable time of lack of fights.
Once tipped as the rising talent of British boxing, he now finds himself trying to achieve expectations - maybe in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors willing to be aggressive in a tentative early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in 2022 after breaking his hand mid-fight, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for Buatsi, who utilized a solid defense to edge the more effective rounds.
The crowd's patience decreased because of frequent holding, with the challenger going down multiple occasions during clinches.
Parker finished the stronger, but multiple periods were challenging to assess. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a excellent Manchester vs Manchester fight to win the continental championship.
The venue fell silent for a deeply poignant tribute prior to the bout as 10 bells tolled in honor of the city's native Ricky Hatton, who passed away 46 years old in recently.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the last bell ended, the quiet transitioned to a roar of "only one Ricky Hatton".
The fighting within the ring reflected the feeling. The eventual winner was floored by a left hook flush on the jaw in the early round, rising shakily to his position on the eight count.
But the traditional red equipment of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was injured early, heavy swelling appearing under his face as the fighters landed hard punches.
The challenger, 27, connected with strong blows but Arthur, 34, responded in kind with powerful upward punches as the pace hardly diminished over twelve rounds.
The victor narrowly won the result with scoring tallies of even score, 115-113 and wider gap, but both fighters were determined and courageous, everything their idol the legend embodied.