British light-heavyweight Buatsi earned a win yet underwhelming debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a close ten-round fight at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful clean blows in a fight where the approaches never quite clicked, with excessive holding disrupting the contest.
The officials judged it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my greatest showing but what defines champions? They win," the victor commented in the arena as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts thought the challenger, 31, should have been awarded the win but the British boxer suffered the second setback of his 28-fight professional journey.
Buatsi Secures Win in Dull Match
His career development has slowed in recent years through management issues and considerable time of inactivity.
Previously predicted as the future of British boxing, he now finds himself trying to realize his potential - possibly in what seems like a last chance - under recent support.
He opened tentatively, with the two boxers prepared to overcommit in a cagey opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was making just his second bout at light heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who worked behind a protective stance to narrowly win the more effective periods.
The audience's tolerance wore thin because of regular grabbing, with the challenger falling to the floor multiple occasions during clinches.
Parker closed well, but many rounds were challenging to assess. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Hatton Homage Motivates Manchester Derby Battle
In the co-main event, Arthur defeated Rea by divided decision in a outstanding local rivalry contest to secure the continental championship.
The arena grew hushed for a extremely emotional homage before the fight as a bell ceremony rang in memory of Manchester's own Ricky Hatton, who died 46 years old in recently.
It was the premier televised boxing event in the location since Hatton's death. As the concluding sound ended, the silence gave way to a shout of "there's just one Ricky Hatton".
The fighting during the bout reflected the feeling. The eventual winner was knocked down by a significant blow squarely on the jaw in the initial stage, standing uncertainly to his position on the eight count.
But the traditional red attire of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was damaged quickly, heavy swelling appearing under his orbital area as the duo traded punishing blows.
Rea, 27, connected with strong blows but the champion, 34, fought fire with fire with powerful upward punches as the intensity rarely dropped over 12 rounds.
Arthur barely secured the decision with judges scorecards of draw, narrow lead and 115-112, but each competitor were persistent and full of heart, all the qualities their inspiration the legend represented.
