UK light-heavyweight Buatsi made a winning yet underwhelming start to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a majority decision in a tight 10-round bout at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful individual punches in a fight where the styles failed to mesh, with frequent clinching disrupting the contest.
The scoring judges judged it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They prevail," Buatsi commented in the ring as he was met by negative reactions from the crowd.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in February - to earn a 20th career victory.
Some ringside observers believed Parker, thirty-one, deserved the win but the Derbyshire fighter suffered the second setback of his 28-match career.
The Champion Secures Victory in Uneventful Affair
His career development has stalled in recent years through promotional disputes and extended periods of lack of fights.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to achieve expectations - possibly in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers ready to overcommit in a tentative early stages.
Parker, whose sole prior loss came at the lower weight class against John Ryder in 2022 after breaking his hand mid-fight, was making just his second fight at the higher weight class.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who operated with a solid defense to barely take the better periods.
The audience's tolerance wore thin during regular grabbing, with Parker slipping to the canvas various instances during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. Although, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the likes of power puncher David Benavidez, and Russian star Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Motivates Local Rivalry Fight
In the secondary fight, Arthur overcame Rea by split-decision in a terrific Manchester vs Manchester fight to capture the European light-heavyweight title.
The arena grew hushed for a deeply poignant tribute prior to the bout as 10 bells sounded in honor of the city's native Ricky Hatton, who died at age 46 in last month.
It was the initial significant broadcast match card in the location since Hatton's passing. As the final chime faded, the silence transitioned to a shout of "there's just one Hatton".
The competition within the ring equaled the feeling. The eventual winner was floored by a significant blow flush on the face in the early round, rising shakily to his footing on the count of eight.
But the Manchester United-red equipment of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was marked up soon, significant bruising developing under his orbital area as the fighters exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the pace hardly diminished over 12 rounds.
Arthur edged the verdict with judges scorecards of even score, narrow lead and 115-112, but the two athletes were relentless and courageous, exactly what their hero Hatton represented.
