British light-heavyweight Buatsi secured a victory yet disappointing debut to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a split decision in a competitive ten-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful individual punches in a contest where the techniques didn't complement each other, with constant grabbing disrupting the contest.
The officials judged it 96-94 to the winner, with the final judge a even score.
"It wasn't my finest showing but how do champions respond? They succeed," Buatsi commented in the ringside as he was faced negative reactions from the crowd.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, merited the win but the Derbyshire fighter suffered the second setback of his 28-match career.
The Champion Claims Triumph in Uneventful Match
The fighter's advancement has plateaued in recent years through promotional disputes and considerable time of inactivity.
Previously predicted as the next star of British boxing, he now finds himself trying to realize his potential - maybe in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers willing to be aggressive in a tentative initial rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after damaging his hand in the contest, was participating in his second appearance at light heavyweight.
By the halfway stage, Parker had stayed in contention, making life awkward for Buatsi, who worked behind a tight guard to barely take the cleaner stanzas.
The crowd's patience decreased during regular grabbing, with the challenger slipping to the canvas various instances during clinches.
Parker ended stronger, but multiple periods were challenging to assess. Nevertheless, former world champion the boxing analyst - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor advances, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Homage Motivates Manchester Derby Battle
In the secondary fight, Arthur overcame Bradley Rea by close verdict in a excellent Manchester vs Manchester battle to capture the continental title.
The venue fell silent for a profoundly moving memorial ahead of the contest as 10 bells sounded in honor of local hero Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the final chime faded, the quiet became a chant of "there's just one Hatton".
The fighting inside the ropes matched the feeling. The eventual winner was floored by a left hook flush on the face in the early round, rising shakily to his footing on the count of eight.
But the traditional red equipment of Arthur soon pressed ahead again. Across the ring, Rea - in opposing blue - was injured quickly, noticeable damage appearing under his orbital area as the fighters exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the pace seldom decreased over twelve rounds.
The victor edged the verdict with scoring tallies of 114-114, narrow lead and wider gap, but each competitor were determined and full of heart, all the qualities their inspiration the legend represented.
