UK light-heavyweight Buatsi made a winning yet underwhelming start to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a close ten-round bout at the Co-op Live Arena.
But Parker had his moments, connecting with powerful clean blows in a contest where the styles didn't complement each other, with constant grabbing disrupting the fight.
The scoring judges had it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my best display but what do champions do? They succeed," Buatsi said in the arena as he was met by negative reactions from the spectators.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to claim a 20th pro success.
Some ringside observers believed the challenger, 31, merited the victory but the contender suffered the second setback of his 28-match professional journey.
Buatsi Secures Victory in Uneventful Encounter
His career development has slowed in recent years through management issues and long spells of lack of fights.
Earlier forecast as the future of British boxing, he now finds himself trying to realize his potential - perhaps in what feels like a final roll of the dice - under new promotional backing.
He began cautiously, with both competitors willing to take risks in a tentative early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after damaging his hand mid-fight, was making just his second appearance at the higher weight class.
By the halfway stage, the underdog had kept it close, creating difficulties for the favorite, who utilized a protective stance to narrowly win the cleaner periods.
The spectators' acceptance decreased amid frequent holding, with Parker going down various instances during clinches.
The underdog finished the stronger, but many rounds were challenging to assess. However, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
The victor moves on, but with the presence of heavy hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - judging by this showing - still appears challenging.
Hatton Memorial Fuels All-Manchester Fight
In the supporting bout, Arthur overcame Rea by divided decision in a outstanding Manchester vs Manchester battle to capture the European light-heavyweight title.
The venue grew hushed for a extremely emotional memorial prior to the bout as a bell ceremony tolled in memory of the city's native Ricky Hatton, who passed away aged 46 in September.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the concluding sound disappeared, the silence gave way to a roar of "there's just one Ricky Hatton".
The competition during the bout reflected the emotion. The eventual winner was knocked down by a significant blow squarely on the face in the initial stage, standing uncertainly to his position on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was marked up soon, significant bruising forming under his orbital area as the duo traded punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the intensity hardly diminished over 12 rounds.
The victor barely secured the decision with scoring tallies of draw, narrow lead and clearer margin, but both fighters were determined and full of heart, all the qualities their idol Hatton represented.
