UK light heavyweight Buatsi earned a win yet disappointing start to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a close 10-round contest at the Manchester venue.
But the challenger landed significant shots, delivering effective individual punches in a contest where the styles never quite clicked, with constant grabbing disrupting the action.
The scoring judges judged it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my finest showing but what defines champions? They win," the victor stated in the arena as he was met by negative reactions from the crowd.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to secure a 20th career victory.
Various analysts felt the challenger, thirty-one, should have been awarded the decision but the Derbyshire fighter suffered the second setback of his 28-bout career.
The Champion Claims Triumph in Uneventful Encounter
The fighter's advancement has stalled in the past few years through promotional disputes and considerable time of inactivity.
Once tipped as the rising talent of the British fight scene, he now stands trying to achieve expectations - possibly in what seems like a final roll of the dice - under recent support.
He opened tentatively, with neither fighter ready to be aggressive in a calculated initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was participating in his second fight at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a tight guard to barely take the cleaner rounds.
The crowd's patience diminished amid regular grabbing, with the challenger falling to the floor several times during grappling.
The underdog ended stronger, but multiple periods were difficult to score. 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 hard hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Hatton Tribute Fuels Local Rivalry Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific local rivalry battle to secure the European light-heavyweight title.
The stadium fell silent for a deeply poignant tribute ahead of the contest as ten bells rang in honor of local hero Ricky Hatton, who passed away aged 46 in September.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the final chime ended, the stillness became a roar of "there's only one Hatton".
The competition inside the ropes equaled the feeling. The eventual winner was sent to the canvas by a powerful punch directly to the face in the initial stage, standing uncertainly to his position on the referee's count.
But the red-colored attire of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was injured early, noticeable damage forming under his orbital area as the fighters landed powerful shots.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with effective uppercuts as the action rarely dropped over 12 rounds.
The victor narrowly won the decision with scoring tallies of draw, narrow lead and clearer margin, but both fighters were relentless and full of heart, everything their inspiration the legend stood for.
