British light-heavyweight Buatsi earned a win yet unimpressive start to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close ten-round bout at the boxing arena.
But Parker found success, connecting with powerful clean blows in a match where the styles failed to mesh, with excessive holding disrupting the fight.
The officials judged it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my best showing but how do champions respond? They prevail," Buatsi said in the ring as he was greeted with boos from the audience.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a twentieth professional win.
Some ringside observers believed Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter suffered the second loss of his 28-match career.
Buatsi Claims Victory in Slow Encounter
Buatsi's progress has stalled in the past few years through promotional disputes and long spells of lack of fights.
Earlier forecast as the next star of UK boxing, he now stands trying to realize his potential - perhaps in what feels like a final roll of the dice - under recent support.
He started carefully, with neither fighter ready to overcommit in a cagey initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second fight at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a tight guard to narrowly win the cleaner periods.
The spectators' acceptance diminished amid constant clinching, with the challenger going down various instances during close exchanges.
The underdog closed well, but many rounds were difficult to score. Although, former world champion the boxing analyst - working with Dazn - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the likes of heavy hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Tribute Inspires Manchester Derby Contest
In the supporting bout, Lyndon Arthur beat Rea by divided decision in a terrific all-Manchester fight to win the European light-heavyweight championship.
The venue grew hushed for a extremely emotional homage ahead of the contest as a bell ceremony tolled in honor of Manchester's own Hatton, who succumbed aged 46 in last month.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the last bell disappeared, the quiet gave way to a shout of "there's just one Ricky Hatton".
The competition within the ring matched the emotion. Arthur was sent to the canvas by a powerful punch flush on the jaw in the second round, standing uncertainly to his position on the eight count.
But the red-colored attire of Arthur soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up soon, noticeable damage developing under his orbital area as the duo landed punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the action seldom decreased over twelve rounds.
Arthur narrowly won the result with judges scorecards of 114-114, 115-113 and clearer margin, but each competitor were relentless and brave, exactly what their inspiration Hatton represented.
