British light-heavyweight Buatsi made a winning yet unimpressive start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a majority decision in a close ten-round fight at the boxing arena.
But Parker had his moments, landing some telling single shots in a contest where the approaches didn't complement each other, with excessive holding disrupting the action.
The scoring judges judged it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my finest performance but how do champions respond? They succeed," the victor said in the arena as he was faced boos from the spectators.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Various analysts thought Parker, thirty-one, deserved the win but the British boxer suffered the second loss of his 28-match professional journey.
The Champion Secures Victory in Dull Affair
The fighter's advancement has plateaued in the past few years through management issues and extended periods of inactivity.
Earlier forecast as the future of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a last chance - under recent support.
He started carefully, with both competitors ready to overcommit 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 during the bout, was making just his second fight at light heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who operated with a protective stance to narrowly win the better periods.
The audience's tolerance decreased during frequent holding, with the challenger going down multiple occasions during clinches.
The underdog closed well, but multiple periods were hard to judge. Although, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, giving Buatsi just one round.
Buatsi advances, but with the caliber of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - judging by this showing - still looks steep.
Hatton Memorial Fuels All-Manchester Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by split-decision in a terrific all-Manchester fight to capture the European light heavyweight championship.
The stadium became quiet for a extremely emotional homage before the fight as a bell ceremony rang in memory of Manchester's own Hatton, who died 46 years old in last month.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the last bell disappeared, the stillness became a chant of "only one Hatton".
The action within the ring matched the feeling. Arthur was floored by a left hook directly to the chin in the initial stage, standing uncertainly to his position on the referee's count.
But the red-colored equipment of the fighter soon pressed ahead again. From the other corner, the opponent - in opposing blue - was marked up quickly, heavy swelling forming under his face as the fighters exchanged punishing blows.
Rea, twenty-seven, landed power punches but Arthur, 34, matched the intensity with effective uppercuts as the action rarely dropped over twelve rounds.
Arthur edged the verdict with scoring tallies of 114-114, 115-113 and clearer margin, but each competitor were determined and courageous, exactly what their inspiration the legend stood for.
