UK light-heavyweight Buatsi made a winning yet unimpressive start to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a competitive 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective single shots in a match where the techniques never quite clicked, with excessive holding disrupting the action.
The scoring judges had it 96-94 in favor to the winner, with the third a even score.
"It wasn't my greatest showing but how do champions respond? They succeed," the victor said in the ring as he was greeted with negative reactions from the crowd.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Various analysts felt the challenger, 31, deserved the win but the contender experienced the second loss of his 28-fight professional journey.
Buatsi Secures Triumph in Dull Affair
The fighter's advancement has slowed in recent times through contract problems and considerable time of inactivity.
Earlier forecast as the future of British boxing, he now stands trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with neither fighter 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 damaging his hand mid-fight, was making just his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a tight guard to edge the more effective rounds.
The audience's tolerance diminished during frequent holding, with the challenger slipping to the canvas multiple occasions during close exchanges.
Parker ended stronger, but many rounds were difficult to score. Although, previous titleholder Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor progresses, but with the likes of power puncher Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Ricky Hatton Memorial Motivates Manchester Derby Contest
In the secondary fight, Arthur overcame Rea by close verdict in a outstanding Manchester vs Manchester contest to secure the European light heavyweight belt.
The stadium fell silent for a extremely emotional tribute ahead of the contest as 10 bells sounded in remembrance of Manchester's own Hatton, who died 46 years old in recently.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the last bell faded, the quiet became a roar of "there's just one Ricky Hatton".
The competition within the ring equaled the sentiment. Arthur was knocked down by a powerful punch directly to the face in the initial stage, standing uncertainly to his feet on the referee's count.
But the traditional red equipment of the fighter soon came forward again. Across the ring, the opponent - in competitive blue - was marked up soon, heavy swelling appearing under his face as the fighters exchanged punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with effective uppercuts as the intensity hardly diminished over 12 rounds.
Arthur edged the result with official scores of even score, close margin and wider gap, but the two athletes were relentless and courageous, everything their idol the legend stood for.
