British light-heavyweight Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a tight ten-round fight at the Manchester venue.
But the challenger found success, landing some telling individual punches in a match where the styles failed to mesh, with constant grabbing disrupting the contest.
Two judges had it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my greatest performance but what defines champions? They succeed," the victor stated in the arena as he was met by boos from the crowd.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts felt the challenger, thirty-one, deserved the decision but the British boxer experienced the second setback of his 28-bout career.
Buatsi Secures Victory in Dull Affair
The fighter's advancement has slowed in the past few years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with neither fighter willing to overcommit in a calculated initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after breaking his hand in the contest, was participating in his second appearance at the higher weight class.
By the halfway stage, Parker had kept it close, causing problems for Buatsi, who operated with a solid defense to barely take the cleaner rounds.
The spectators' acceptance decreased because of constant clinching, with Parker slipping to the canvas multiple occasions during grappling.
The underdog closed well, but multiple periods were hard to judge. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor progresses, but with the presence of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Tribute Motivates Local Rivalry Fight
In the secondary fight, Arthur beat Bradley Rea by close verdict in a excellent Manchester vs Manchester battle to win the European light-heavyweight belt.
The venue grew hushed for a extremely emotional memorial before the fight as ten bells rang in honor of local hero Hatton, who died aged 46 in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the last bell faded, the stillness transitioned to a shout of "only one Ricky Hatton".
The action within the ring matched the sentiment. Arthur was sent to the canvas by a powerful punch squarely on the chin in the second round, standing uncertainly to his feet on the count of eight.
But the red-colored shorts of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was damaged quickly, significant bruising developing under his face as the fighters landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with stinging uppercuts as the intensity seldom decreased over the full distance.
Arthur narrowly won the decision with judges scorecards of 114-114, close margin and clearer margin, but each competitor were persistent and full of heart, all the qualities their hero the legend stood for.
