British light-heavyweight Buatsi earned a win yet underwhelming beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a majority decision in a competitive 10-round fight at the boxing arena.
But Parker found success, connecting with powerful single shots in a contest where the styles didn't complement each other, with excessive holding disrupting the contest.
The officials scored it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best display but what do champions do? They prevail," the victor commented in the ring 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 his previous opponent in last winter - to secure a 20th career victory.
Some ringside observers thought Parker, 31, deserved the decision but the Derbyshire fighter suffered the second setback of his 28-fight career.
Buatsi Claims Victory in Uneventful Encounter
Buatsi's progress has stalled in recent years through promotional disputes and considerable time of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under recent support.
He began cautiously, with both competitors prepared to overcommit in a tentative early stages.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was making just his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a tight guard to narrowly win the more effective stanzas.
The crowd's patience decreased because of constant clinching, with the challenger going down multiple occasions during close exchanges.
The underdog closed well, but many rounds were difficult to score. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just one round.
The victor progresses, but with the likes of power puncher David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Hatton Homage Inspires All-Manchester Fight
In the secondary fight, Lyndon Arthur defeated Rea by close verdict in a terrific Manchester vs Manchester battle to win the European light-heavyweight belt.
The stadium fell silent for a extremely emotional tribute prior to the bout as 10 bells sounded in honor of Manchester's own Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the concluding sound ended, the stillness gave way to a roar of "there's just one Hatton".
The action inside the ropes reflected the sentiment. Arthur was floored by a significant blow directly to the jaw in the initial stage, getting up unsteadily to his feet on the referee's count.
But the traditional red equipment of the fighter soon came forward again. Across the ring, the opponent - in competitive blue - was injured early, significant bruising developing under his face as the fighters exchanged hard punches.
The challenger, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with stinging uppercuts as the action rarely dropped over 12 rounds.
Arthur narrowly won the verdict with scoring tallies of even score, narrow lead and clearer margin, but both fighters were determined and brave, exactly what their hero Hatton represented.
