UK light heavyweight Buatsi made a winning yet disappointing start to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a close 10-round contest at the Manchester venue.
But Parker found success, landing some telling single shots in a match where the styles never quite clicked, with constant grabbing spoiling the action.
The scoring judges had it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best performance but what do champions do? They prevail," the victor commented in the ring as he was met by negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts thought the challenger, thirty-one, should have been awarded the win but the contender endured the second setback of his 28-fight career.
Buatsi Claims Victory in Uneventful Encounter
The fighter's advancement has slowed in the past few years through management issues and long spells of lack of fights.
Once tipped as the future of British boxing, he now is positioned trying to realize his potential - perhaps in what feels like a ultimate opportunity - under fresh management.
He started carefully, with neither fighter ready to be aggressive in a tentative early stages.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was participating in his second appearance at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a protective stance to narrowly win the better periods.
The crowd's patience diminished during frequent holding, with Parker slipping to the canvas several times during clinches.
The underdog ended stronger, but several stanzas were hard to judge. However, former world champion Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, giving Buatsi just one round.
Buatsi moves on, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Homage Motivates All-Manchester Fight
In the secondary fight, Lyndon Arthur overcame Bradley Rea by close verdict in a excellent all-Manchester fight to win the European light heavyweight title.
The venue grew hushed for a extremely emotional memorial ahead of the contest as 10 bells rang in honor of Manchester's own Hatton, who passed away at age 46 in recently.
It was the premier televised boxing event in the location since Hatton's death. As the final chime faded, the stillness became a shout of "there's only one Hatton".
The competition inside the ropes reflected the feeling. Arthur was knocked down by a significant blow flush on the face in the early round, rising shakily to his position on the referee's count.
But the red-colored equipment of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was injured soon, significant bruising forming under his face as the duo landed powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity hardly diminished over the full distance.
The victor barely secured the result with scoring tallies of 114-114, close margin and 115-112, but the two athletes were persistent and full of heart, all the qualities their inspiration the legend stood for.
