UK light heavyweight Buatsi secured a victory yet unimpressive start to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a majority decision in a tight 10-round bout at the Manchester venue.
But the challenger landed significant shots, landing some telling individual punches in a contest where the techniques didn't complement each other, with excessive holding disrupting the contest.
Two judges judged it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my best performance but what do champions do? They succeed," Buatsi commented in the ringside as he was faced disapproval from the audience.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to claim a 20th career victory.
Some ringside observers believed Parker, 31, should have been awarded the decision but the British boxer experienced the second loss of his 28-bout career.
Buatsi Claims Victory in Slow Encounter
His career development has stalled in recent times through management issues and long spells of lack of fights.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to realize his potential - possibly in what feels like a last chance - under new promotional backing.
He began cautiously, with neither fighter ready to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was making just his second appearance at the higher weight class.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to barely take the more effective stanzas.
The crowd's patience wore thin amid constant clinching, with the challenger falling to the floor several times during grappling.
Parker ended stronger, but several stanzas were challenging to assess. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just a single round.
The victor advances, but with the likes of power puncher Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - judging by this showing - still appears challenging.
Hatton Tribute Motivates Local Rivalry Contest
In the supporting bout, Lyndon Arthur beat Rea by divided decision in a excellent all-Manchester fight to win the European light-heavyweight title.
The stadium fell silent for a deeply poignant homage prior to the bout as ten bells sounded in honor of Manchester's own Ricky Hatton, who succumbed 46 years old in recently.
It was the premier televised match card in the urban center since the passing of Hatton. As the last bell disappeared, the quiet gave way to a shout of "there's only one Ricky Hatton".
The action during the bout matched the feeling. The eventual winner was sent to the canvas by a significant blow directly to the face in the initial stage, standing uncertainly to his footing on the referee's count.
But the traditional red equipment of the fighter soon pressed ahead again. From the other corner, the opponent - in opposing blue - was marked up quickly, significant bruising appearing under his face as the fighters exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with effective uppercuts as the action seldom decreased over 12 rounds.
Arthur narrowly won the result with official scores of 114-114, narrow lead and 115-112, but the two athletes were persistent and courageous, all the qualities their hero Hatton embodied.
