British 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 bronze medallist's work rate seemingly secured him a judges' verdict in a close 10-round fight at the Manchester venue.
But Parker found success, connecting with powerful single shots in a match where the approaches never quite clicked, with frequent clinching disrupting the action.
The officials judged it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They succeed," the victor said in the ringside as he was greeted with disapproval from the spectators.
The British fighter bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Several boxing experts believed Parker, 31, should have been awarded the decision but the contender endured the second setback of his 28-match professional journey.
Buatsi Claims Triumph in Dull Encounter
The fighter's advancement has slowed in recent times through promotional disputes and extended periods of inactivity.
Once tipped as the rising talent of UK boxing, he now finds himself trying to realize his potential - maybe in what feels like a final roll of the dice - under recent support.
He started carefully, with both competitors willing to overcommit in a cagey early stages.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand in the contest, was making just his second appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who worked behind a protective stance to narrowly win the better rounds.
The audience's tolerance wore thin during frequent holding, with Parker slipping to the canvas several times during close exchanges.
Parker finished the stronger, but many rounds were difficult to score. Nevertheless, former world champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the likes of hard hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - judging by this showing - still seems difficult.
Hatton Homage Fuels All-Manchester Contest
In the co-main event, Arthur beat Bradley Rea by split-decision in a outstanding local rivalry fight to win the European light-heavyweight championship.
The arena became quiet for a deeply poignant homage prior to the bout as ten bells tolled in honor of local hero Ricky Hatton, who passed away 46 years old in September.
It was the first major televised match card in the city since the passing of Hatton. As the concluding sound ended, the quiet gave way to a shout of "there's just one Hatton".
The action inside the ropes matched the emotion. Arthur was floored by a significant blow directly to the chin in the early round, rising shakily to his position on the eight count.
But the red-colored shorts of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was marked up quickly, noticeable damage forming under his face as the pair exchanged hard punches.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over twelve rounds.
Arthur edged the decision with official scores of 114-114, close margin and wider gap, but the two athletes were relentless and brave, all the qualities their hero Hatton represented.
