British light-heavyweight Buatsi earned a win yet unimpressive debut to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a tight ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective single shots in a fight where the techniques never quite clicked, with constant grabbing disrupting the action.
The officials had it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my finest display but how do champions respond? They prevail," the victor stated in the arena as he was greeted with negative reactions from the audience.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to claim a twentieth professional win.
Various analysts thought Parker, thirty-one, should have been awarded the win but the Derbyshire fighter endured the second loss of his 28-bout career.
The Champion Claims Win in Dull Affair
His career development has plateaued in recent times through promotional disputes and considerable time of inactivity.
Once tipped as the next star of British boxing, he now stands trying to realize his potential - possibly in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with the two boxers prepared to take risks in a tentative early stages.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second bout at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, causing problems for the favorite, who operated with a solid defense to edge the better rounds.
The audience's tolerance decreased during constant clinching, with the challenger going down various instances during close exchanges.
Parker finished the stronger, but multiple periods were hard to judge. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Memorial Inspires All-Manchester Battle
In the supporting bout, Arthur beat Bradley Rea by close verdict in a outstanding Manchester vs Manchester fight to capture the European light heavyweight title.
The stadium grew hushed for a profoundly moving tribute before the fight as ten bells rang in honor of Manchester's own Hatton, who passed away at age 46 in September.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the last bell faded, the quiet became a roar of "there's only one Ricky Hatton".
The action inside the ropes matched the feeling. The eventual winner was sent to the canvas by a significant blow flush on the jaw in the early round, getting up unsteadily to his footing on the referee's count.
But the red-colored attire of the fighter soon pressed ahead again. From the other corner, Rea - in competitive blue - was damaged early, significant bruising appearing under his orbital area as the pair landed hard punches.
The challenger, 27, connected with strong blows but the champion, 34, responded in kind with effective uppercuts as the action rarely dropped over 12 rounds.
The victor barely secured the decision with official scores of even score, narrow lead and clearer margin, but each competitor were persistent and brave, exactly what their idol Hatton embodied.
