British light-heavyweight Buatsi earned a win yet unimpressive start to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a close 10-round bout at the boxing arena.
But Parker landed significant shots, landing some telling individual punches in a fight where the styles never quite clicked, with constant grabbing disrupting the contest.
The officials judged it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best performance but what defines champions? They succeed," the victor stated in the ringside as he was faced boos from the spectators.
The British fighter returned to winning ways after his initial pro loss - an epic battle with Callum Smith in February - to secure a 20th career victory.
Several boxing experts believed the challenger, 31, deserved the victory but the Derbyshire fighter endured the second loss of his 28-fight professional journey.
The Champion Secures Victory in Uneventful Encounter
Buatsi's progress has slowed in recent years through promotional disputes and considerable time of inactivity.
Once tipped as the rising talent of British boxing, he now stands trying to fulfil that early promise - perhaps in what seems like a ultimate opportunity - under fresh management.
He started carefully, with both competitors ready to be aggressive in a calculated early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after damaging his hand during the bout, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a protective stance to edge the better stanzas.
The spectators' acceptance wore thin during constant clinching, with the challenger going down multiple occasions during clinches.
Parker finished the stronger, but many rounds were hard to judge. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for Parker, awarding Buatsi just one round.
The victor progresses, but with the likes of hard hitter David Benavidez, and Russian champion Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Homage Inspires All-Manchester Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding local rivalry battle to secure the European light-heavyweight belt.
The venue became quiet for a deeply poignant tribute ahead of the contest as 10 bells rang in memory of Manchester's own Ricky Hatton, who succumbed aged 46 in last month.
It was the premier televised match card in the city since Hatton's passing. As the last bell faded, the quiet became a shout of "there's just one Hatton".
The fighting within the ring equaled the emotion. The eventual winner was knocked down by a left hook directly to the jaw in the initial stage, getting up unsteadily to his position on the eight count.
But the red-colored attire of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was injured early, significant bruising forming under his eye as the duo exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the intensity rarely dropped over the full distance.
The victor barely secured the result with official scores of draw, close margin and 115-112, but each competitor were determined and full of heart, everything their idol Hatton represented.
