British light heavyweight Buatsi earned a win yet underwhelming start to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a close 10-round bout at the Manchester venue.
But Parker landed significant shots, connecting with powerful individual punches in a contest where the approaches didn't complement each other, with excessive holding spoiling the action.
Two judges judged it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest performance but how do champions respond? They win," Buatsi commented in the arena as he was met by boos from the audience.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in February - to claim a 20th pro success.
Various analysts felt the challenger, thirty-one, deserved the decision but the Derbyshire fighter experienced the second loss of his 28-fight career.
The Champion Claims Triumph in Dull Match
The fighter's advancement has slowed in recent years through management issues and extended periods of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to realize his potential - possibly in what feels like a last chance - under new promotional backing.
He started carefully, with the two boxers ready to be aggressive in a cagey early stages.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand in the contest, was making just his second appearance at light-heavyweight.
By the halfway stage, Parker had made it competitive, making life awkward for Buatsi, who operated with a solid defense to barely take the more effective stanzas.
The audience's tolerance diminished during frequent holding, with the challenger going down several times during grappling.
The underdog closed well, but many rounds were challenging to assess. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of power puncher David Benavidez, and Russian champion Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Homage Motivates Manchester Derby Battle
In the secondary fight, Lyndon Arthur beat Rea by close verdict in a terrific all-Manchester battle to secure the European light-heavyweight belt.
The venue became quiet for a profoundly moving memorial prior to the bout as 10 bells sounded in memory of the city's native Hatton, who passed away at age 46 in last month.
It was the premier televised match card in the location since the passing of Hatton. As the concluding sound faded, the silence became a chant of "there's only one Ricky Hatton".
The competition within the ring equaled the emotion. Arthur was floored by a significant blow directly to the jaw in the second round, getting up unsteadily to his feet on the count of eight.
But the red-colored equipment of Arthur soon advanced again. Across the ring, the opponent - in competitive blue - was damaged early, noticeable damage forming under his face as the pair landed powerful shots.
The challenger, 27, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the intensity seldom decreased over twelve rounds.
The victor edged the decision with scoring tallies of draw, narrow lead and clearer margin, but both fighters were persistent and full of heart, everything their inspiration the legend embodied.
