UK light heavyweight Buatsi secured a victory yet underwhelming debut to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a close ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling single shots in a match where the techniques didn't complement each other, with constant grabbing disrupting the action.
The officials judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my best display but what defines champions? They prevail," the victor stated in the ringside as he was faced disapproval from the crowd.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Various analysts thought the challenger, 31, deserved the victory but the contender experienced the second setback of his 28-fight career.
Buatsi Claims Victory in Uneventful Affair
His career development has slowed in recent times through promotional disputes and extended periods of lack of fights.
Previously predicted as the rising talent of UK boxing, he now stands trying to realize his potential - maybe in what feels like a final roll of the dice - under recent support.
He opened tentatively, with both competitors ready to take risks in a cagey early stages.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was making just his second fight at light-heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for Buatsi, who utilized a solid defense to edge the better stanzas.
The audience's tolerance diminished amid frequent holding, with Parker slipping to the canvas several times during close exchanges.
Parker finished the stronger, but multiple periods were challenging to assess. However, ex-champion Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of power puncher David Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Homage Fuels All-Manchester Fight
In the supporting bout, Lyndon Arthur overcame Rea by split-decision in a excellent Manchester vs Manchester fight to secure the European light-heavyweight belt.
The venue fell silent for a extremely emotional tribute prior to the bout as 10 bells sounded in honor of the city's native Hatton, who died at age 46 in recently.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the concluding sound disappeared, the quiet transitioned to a roar of "there's just one Hatton".
The fighting inside the ropes matched the sentiment. The eventual winner was floored by a significant blow directly to the jaw in the initial stage, getting up unsteadily to his footing on the referee's count.
But the traditional red equipment of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was damaged early, significant bruising appearing under his eye as the duo traded hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace hardly diminished over 12 rounds.
The victor barely secured the decision with official scores of 114-114, 115-113 and clearer margin, but both fighters were relentless and full of heart, everything their hero Hatton stood for.
