British light-heavyweight Buatsi earned a win yet unimpressive start to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But the challenger had his moments, landing some telling single shots in a fight where the styles never quite clicked, with constant grabbing disrupting the contest.
The officials judged it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my greatest performance but what defines champions? They succeed," the victor stated in the ringside as he was faced disapproval from the crowd.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in February - to claim a 20th pro success.
Several boxing experts believed Parker, 31, deserved the victory but the Derbyshire fighter experienced the second loss of his 28-match career.
Buatsi Earns Win in Dull Match
The fighter's advancement has plateaued in recent years through contract problems and extended periods of lack of fights.
Once tipped as the next star of British boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter ready to overcommit in a cagey early stages.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand in the contest, was competing in only his second bout at light-heavyweight.
By the middle rounds, the underdog had kept it close, causing problems for Buatsi, who utilized a solid defense to narrowly win the more effective rounds.
The crowd's patience diminished because of constant clinching, with Parker going down multiple occasions during clinches.
Parker closed well, but several stanzas were difficult to score. However, former world champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Tribute Motivates Local Rivalry Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by split-decision in a outstanding all-Manchester fight to capture the continental belt.
The venue fell silent for a deeply poignant homage ahead of the contest as a bell ceremony rang in memory of local hero Ricky Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the last bell disappeared, the stillness became a chant of "only one Ricky Hatton".
The action during the bout matched the emotion. Arthur was knocked down by a significant blow directly to the chin in the second round, getting up unsteadily to his position on the count of eight.
But the traditional red equipment of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was injured quickly, significant bruising forming under his face as the duo landed hard punches.
Rea, 27, connected with strong blows but the champion, 34, fought fire with fire with powerful upward punches as the action seldom decreased over twelve rounds.
The victor barely secured the result with official scores of even score, close margin and clearer margin, but each competitor were relentless and courageous, all the qualities their inspiration Hatton stood for.
