UK light-heavyweight Buatsi earned a win yet underwhelming debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a split decision in a competitive 10-round contest at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful clean blows in a match where the approaches failed to mesh, with constant grabbing disrupting the fight.
Two judges had it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my greatest display but what do champions do? They prevail," the victor said in the arena as he was faced boos from the crowd.
The British fighter bounced back after his first professional defeat - an epic battle with his previous opponent in last winter - to secure a 20th career victory.
Several boxing experts believed the challenger, 31, should have been awarded the decision but the contender endured the second defeat of his 28-bout professional journey.
The Champion Earns Victory in Uneventful Encounter
The fighter's advancement has plateaued in the past few years through promotional disputes and considerable time of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what seems like a last chance - under new promotional backing.
He started carefully, with neither fighter prepared to take risks in a cagey early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in 2022 after breaking his hand during the bout, was participating in his second fight at the higher weight class.
By the middle rounds, the underdog had kept it close, making life awkward for the favorite, who operated with a protective stance to narrowly win the cleaner rounds.
The crowd's patience diminished because of constant clinching, with Parker going down various instances during close exchanges.
Parker ended stronger, but many rounds were hard to judge. However, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor moves on, but with the likes of hard hitter David Benavidez, and Russian champion Bivol leading the category, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Memorial Fuels Local Rivalry Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding Manchester vs Manchester fight to win the European light-heavyweight championship.
The stadium grew hushed for a extremely emotional memorial before the fight as ten bells tolled in honor of the city's native Ricky Hatton, who succumbed 46 years old in last month.
It was the first major televised fight night in the city since the passing of Hatton. As the concluding sound ended, the silence became a roar of "there's just one Ricky Hatton".
The fighting within the ring equaled the emotion. Arthur was knocked down by a powerful punch squarely on the chin in the second round, standing uncertainly to his feet on the eight count.
But the traditional red equipment of Arthur soon came forward again. On the opposite side, the opponent - in rival City blue - was marked up soon, noticeable damage developing under his orbital area as the duo exchanged punishing blows.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over the full distance.
Arthur narrowly won the decision with official scores of even score, 115-113 and wider gap, but each competitor were determined and brave, exactly what their idol Hatton represented.
