UK light-heavyweight Buatsi earned a win yet disappointing start to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a split decision in a close ten-round contest at the Manchester venue.
But Parker landed significant shots, landing some telling individual punches in a match where the techniques failed to mesh, with excessive holding spoiling the action.
The scoring judges judged it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest performance but what defines champions? They prevail," Buatsi commented in the ringside as he was faced disapproval from the audience.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Various analysts felt the challenger, 31, should have been awarded the win but the contender experienced the second setback of his 28-fight career.
The Champion Secures Triumph in Uneventful Match
His career development has stalled in recent times through promotional disputes and extended periods of lack of fights.
Previously predicted as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under recent support.
He started carefully, with the two boxers willing to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after breaking his hand mid-fight, was participating in his second fight at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who utilized a solid defense to barely take the more effective periods.
The audience's tolerance decreased amid constant clinching, with Parker falling to the floor several times during clinches.
The underdog closed well, but multiple periods were hard to judge. However, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
The victor progresses, but with the presence of power puncher Benavidez, and Russian champion Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Hatton Memorial Fuels Manchester Derby Contest
In the secondary fight, Arthur beat Bradley Rea by divided decision in a outstanding Manchester vs Manchester contest to capture the European light heavyweight title.
The venue fell silent for a profoundly moving homage before the fight as ten bells tolled in honor of the city's native Hatton, who passed away aged 46 in September.
It was the premier televised match card in the location since Hatton's passing. As the last bell disappeared, the silence became a chant of "there's only one Hatton".
The competition during the bout matched the sentiment. The eventual winner was knocked down by a significant blow directly to the chin in the initial stage, standing uncertainly to his footing on the count of eight.
But the red-colored shorts of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was marked up early, significant bruising appearing under his face as the duo exchanged hard punches.
The challenger, 27, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the intensity hardly diminished over 12 rounds.
Arthur narrowly won the decision with judges scorecards of 114-114, close margin and 115-112, but each competitor were determined and courageous, all the qualities their idol Hatton stood for.
