British light heavyweight Buatsi earned a win yet underwhelming beginning to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a split decision in a tight 10-round fight at the boxing arena.
But the challenger had his moments, landing some telling single shots in a match where the styles didn't complement each other, with constant grabbing marring the action.
The officials scored it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest display but what do champions do? They succeed," Buatsi said in the arena as he was greeted with negative reactions from the crowd.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in last winter - to claim a twentieth professional win.
Various analysts believed Parker, thirty-one, merited the decision but the contender suffered the second defeat of his 28-bout professional journey.
Buatsi Claims Triumph in Slow Match
The fighter's advancement has slowed in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now stands trying to fulfil that early promise - possibly in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with the two boxers prepared to take risks in a calculated early stages.
Parker, 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 appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who worked behind a protective stance to barely take the more effective periods.
The crowd's patience wore thin because of constant clinching, with Parker falling to the floor several times during clinches.
The underdog ended stronger, but multiple periods were hard to judge. Nevertheless, ex-champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor advances, but with the caliber of power puncher David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Hatton Homage Fuels Local Rivalry Battle
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding local rivalry battle to secure the continental title.
The venue fell silent for a extremely emotional memorial ahead of the contest as a bell ceremony sounded in honor of local hero Ricky Hatton, who passed away at age 46 in recently.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the final chime faded, the silence became a shout of "there's just one Hatton".
The action inside the ropes reflected the feeling. Arthur was sent to the canvas by a significant blow directly to the jaw in the early round, rising shakily to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was damaged soon, significant bruising appearing under his face as the duo landed powerful shots.
Rea, 27, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the pace hardly diminished over twelve rounds.
Arthur barely secured the decision with official scores of 114-114, narrow lead and clearer margin, but the two athletes were determined and courageous, exactly what their hero Hatton stood for.
