British light heavyweight Buatsi earned a win yet disappointing debut to life under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger found success, delivering effective clean blows in a fight where the styles never quite clicked, with constant grabbing disrupting the fight.
The scoring judges had it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest display but what do champions do? They prevail," Buatsi commented in the ring as he was met by negative reactions from the crowd.
The British fighter got back to winning after his first professional defeat - an memorable fight with his previous opponent in last winter - to earn a 20th career victory.
Various analysts felt the challenger, thirty-one, should have been awarded the victory but the contender experienced the second loss of his 28-bout career.
Buatsi Earns Victory in Slow Affair
The fighter's advancement has slowed in recent years through contract problems and extended periods of lack of fights.
Once tipped as the future of UK boxing, he now stands trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers prepared to be aggressive in a tentative early stages.
Parker, whose single earlier setback came at the lower weight class against his former opponent in 2022 after damaging his hand mid-fight, was making just his second appearance at the higher weight class.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who operated with a solid defense to edge the cleaner periods.
The spectators' acceptance diminished during frequent holding, with the challenger going down several times during grappling.
The underdog ended stronger, but many rounds were hard to judge. Although, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor advances, but with the caliber of power puncher David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Memorial Inspires All-Manchester Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific Manchester vs Manchester battle to secure the European light heavyweight title.
The arena fell silent for a extremely emotional homage prior to the bout as a bell ceremony tolled in honor of local hero Ricky Hatton, who passed away at age 46 in September.
It was the premier televised match card in the location since Hatton's death. As the final chime faded, the silence transitioned to a chant of "there's only one Hatton".
The fighting within the ring reflected the emotion. Arthur was knocked down by a left hook directly to the jaw in the initial stage, standing uncertainly to his footing on the count of eight.
But the red-colored shorts of Arthur soon advanced again. Across the ring, the opponent - in competitive blue - was injured quickly, heavy swelling forming under his eye as the duo exchanged hard punches.
Rea, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over the full distance.
The victor edged the decision with judges scorecards of even score, narrow lead and clearer margin, but the two athletes were persistent and full of heart, exactly what their idol the legend stood for.
