UK light heavyweight Buatsi secured a victory yet disappointing debut to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a close 10-round fight at the Manchester venue.
But the challenger landed significant shots, connecting with powerful clean blows in a contest where the approaches never quite clicked, with frequent clinching spoiling the fight.
The officials judged it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best performance but what do champions do? They succeed," the victor commented in the arena as he was faced boos from the audience.
The Londoner got back to winning after his first professional defeat - an memorable fight with his previous opponent in last winter - to claim a 20th pro success.
Various analysts believed Parker, 31, deserved the win but the Derbyshire fighter experienced the second setback of his 28-bout career.
Buatsi Claims Win in Uneventful Match
The fighter's advancement has slowed in recent times through contract problems and considerable time of lack of fights.
Previously predicted as the rising talent of the British fight scene, he now stands trying to realize his potential - maybe in what seems like a final roll of the dice - under fresh management.
He began cautiously, with neither fighter willing to be aggressive in a calculated initial rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second appearance at light heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a solid defense to narrowly win the more effective stanzas.
The crowd's patience wore thin because of regular grabbing, with Parker going down multiple occasions during clinches.
The underdog finished the stronger, but multiple periods were challenging to assess. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor advances, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Tribute Motivates Local Rivalry Battle
In the secondary fight, Arthur defeated Bradley Rea by close verdict in a terrific all-Manchester fight to capture the continental belt.
The venue became quiet for a profoundly moving memorial prior to the bout as ten bells rang in honor of the city's native Hatton, who passed away aged 46 in recently.
It was the premier televised match card in the urban center since the passing of Hatton. As the concluding sound ended, the silence gave way to a chant of "there's only one Ricky Hatton".
The competition inside the ropes reflected the feeling. Arthur was floored by a significant blow flush on the face in the initial stage, standing uncertainly to his footing on the eight count.
But the Manchester United-red attire of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was injured soon, heavy swelling forming under his face as the pair exchanged punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the pace rarely dropped over twelve rounds.
The victor edged the result with official scores of draw, 115-113 and wider gap, but both fighters were relentless and full of heart, everything their inspiration the legend embodied.
