British light-heavyweight Buatsi earned a win yet unimpressive beginning to his career 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 tight ten-round bout at the boxing arena.
But the challenger found success, delivering effective clean blows in a fight where the techniques failed to mesh, with excessive holding marring the action.
Two judges judged it 96-94 for to the winner, with the final judge a even score.
"It wasn't my greatest performance but what defines champions? They prevail," the victor said in the arena as he was greeted with disapproval from the audience.
The British fighter bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Some ringside observers believed the challenger, thirty-one, deserved the decision but the contender experienced the second defeat of his 28-match career.
Buatsi Claims Victory in Uneventful Encounter
Buatsi's progress has slowed in recent years through promotional disputes and extended periods of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with the two boxers prepared to overcommit in a calculated early stages.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second bout at light heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for Buatsi, who operated with a protective stance to edge the more effective rounds.
The crowd's patience wore thin during constant clinching, with Parker going down various instances during close exchanges.
The underdog closed well, but many rounds were difficult to score. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi moves on, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Homage Motivates All-Manchester Contest
In the co-main event, Lyndon Arthur defeated Bradley Rea by split-decision in a outstanding Manchester vs Manchester contest to secure the European light heavyweight belt.
The venue became quiet for a extremely emotional memorial prior to the bout as a bell ceremony rang in remembrance of Manchester's own Hatton, who passed away aged 46 in last month.
It was the premier televised boxing event in the city since the passing of Hatton. As the final chime disappeared, the silence transitioned to a shout of "there's just one Hatton".
The competition inside the ropes reflected the sentiment. The eventual winner was knocked down by a left hook flush on the face in the initial stage, getting up unsteadily to his footing on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was damaged early, noticeable damage appearing under his eye as the pair exchanged punishing blows.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, responded in kind with powerful upward punches as the intensity hardly diminished over twelve rounds.
Arthur narrowly won the decision with official scores of 114-114, close margin and wider gap, but each competitor were determined and courageous, all the qualities their inspiration Hatton represented.
