British light heavyweight Buatsi earned a win yet unimpressive start to life under new promoters 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 ten-round contest at the boxing arena.
But the challenger landed significant shots, landing some telling clean blows in a fight where the techniques didn't complement each other, with constant grabbing marring the fight.
The officials scored it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my best showing but what defines champions? They succeed," Buatsi commented in the ringside as he was met by negative reactions from the crowd.
The Londoner got back to winning after his first professional defeat - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers felt the challenger, thirty-one, deserved the victory but the British boxer experienced the second setback of his 28-bout career.
Buatsi Earns Win in Slow Encounter
The fighter's advancement has plateaued in recent years through contract problems and considerable time of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what seems like a last chance - under new promotional backing.
He started carefully, with neither fighter ready to overcommit in a cagey initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was making just his second bout at the higher weight class.
By the middle rounds, the underdog had stayed in contention, making life awkward for the favorite, who utilized a tight guard to narrowly win the more effective periods.
The audience's tolerance diminished during frequent holding, with Parker slipping to the canvas various instances during grappling.
Parker finished the stronger, but multiple periods were difficult to score. However, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Memorial Fuels Manchester Derby Fight
In the supporting bout, Arthur beat Bradley Rea by split-decision in a excellent all-Manchester fight to win the European light-heavyweight championship.
The arena became quiet for a extremely emotional memorial ahead of the contest as a bell ceremony tolled in memory of the city's native Hatton, who passed away 46 years old in September.
It was the premier televised match card in the urban center since the passing of Hatton. As the concluding sound faded, the quiet gave way to a chant of "there's just one Ricky Hatton".
The competition inside the ropes equaled the emotion. Arthur was floored by a powerful punch directly to the jaw in the second round, rising shakily to his feet on the referee's count.
But the traditional red attire of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was marked up early, noticeable damage appearing under his orbital area as the pair traded hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the action hardly diminished over 12 rounds.
Arthur edged the verdict with scoring tallies of even score, 115-113 and 115-112, but each competitor were relentless and courageous, everything their hero Hatton stood for.
