British light-heavyweight Buatsi made a winning yet underwhelming start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But Parker landed significant shots, landing some telling clean blows in a fight where the techniques never quite clicked, with frequent clinching disrupting the action.
The scoring judges had it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my finest showing but what do champions do? They win," the victor stated in the arena as he was greeted with disapproval from the spectators.
The Londoner returned to winning ways after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a 20th pro success.
Some ringside observers believed the challenger, thirty-one, merited the win but the contender experienced the second setback of his 28-match professional journey.
Buatsi Secures Win in Dull Affair
Buatsi's progress has stalled in the past few years through promotional disputes and long spells of lack of fights.
Earlier forecast as the next star of UK boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under recent support.
He started carefully, with both competitors prepared to overcommit in a tentative opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was participating in his second fight at the higher weight class.
By the fight's midpoint, Parker had kept it close, causing problems for the favorite, who utilized a tight guard to narrowly win the more effective stanzas.
The audience's tolerance diminished amid frequent holding, with Parker slipping to the canvas multiple occasions during grappling.
Parker ended stronger, but many rounds were hard to judge. Although, former world champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, awarding Buatsi just a single round.
Buatsi moves on, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Homage Inspires Manchester Derby Fight
In the co-main event, Arthur defeated Rea by divided decision in a terrific local rivalry battle to win the continental belt.
The arena grew hushed for a deeply poignant memorial prior to the bout as 10 bells rang in memory of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the initial significant broadcast match card in the location since Hatton's death. As the concluding sound faded, the silence became a shout of "there's only one Ricky Hatton".
The competition during the bout equaled the emotion. The eventual winner was sent to the canvas by a powerful punch squarely on the jaw in the early round, rising shakily to his footing on the count of eight.
But the traditional red equipment of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was damaged quickly, noticeable damage forming under his face as the duo exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the pace seldom decreased over the full distance.
Arthur narrowly won the result with judges scorecards of 114-114, 115-113 and 115-112, but the two athletes were persistent and brave, everything their idol Hatton embodied.
