British light-heavyweight Buatsi made a winning yet underwhelming debut to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a tight ten-round bout at the boxing arena.
But the challenger had his moments, connecting with powerful clean blows in a fight where the approaches failed to mesh, with frequent clinching spoiling the fight.
The scoring judges had it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my best performance but what defines champions? They prevail," the victor stated in the ring as he was faced boos from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers felt the challenger, thirty-one, merited the victory but the contender suffered the second loss of his 28-fight career.
Buatsi Earns Victory in Dull Match
The fighter's advancement has plateaued in recent years through management issues and extended periods of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to realize his potential - perhaps in what seems like a last chance - under recent support.
He opened tentatively, with neither fighter willing to take risks in a cagey initial rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand during the bout, was making just his second bout at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a protective stance to barely take the cleaner periods.
The crowd's patience wore thin amid frequent holding, with the challenger going down several times during clinches.
Parker ended stronger, but many rounds were challenging to assess. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just one round.
The victor advances, but with the likes of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Fuels Manchester Derby Contest
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a outstanding all-Manchester contest to win the continental belt.
The arena fell silent for a extremely emotional homage before the fight as a bell ceremony rang in memory of the city's native Hatton, who succumbed aged 46 in September.
It was the first major televised match card in the urban center since Hatton's death. As the concluding sound disappeared, the stillness became a roar of "only one Hatton".
The fighting inside the ropes reflected the feeling. The eventual winner was floored by a significant blow directly to the chin in the early round, rising shakily to his position on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was injured quickly, noticeable damage appearing under his face as the fighters traded powerful shots.
Rea, 27, landed power punches but the champion, thirty-four, responded in kind with powerful upward punches as the action rarely dropped over the full distance.
The victor narrowly won the decision with official scores of draw, close margin and wider gap, but each competitor were determined and brave, everything their idol Hatton embodied.
