UK light heavyweight Buatsi made a winning yet unimpressive debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a majority decision in a tight ten-round contest at the Manchester venue.
But the challenger had his moments, delivering effective individual punches in a contest where the styles failed to mesh, with excessive holding spoiling the fight.
The officials scored it 96-94 for to the winner, with the third a even score.
"It wasn't my best performance but what defines champions? They win," Buatsi stated in the ring as he was faced negative reactions from the spectators.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a twentieth professional win.
Various analysts felt the challenger, thirty-one, deserved the decision but the contender suffered the second setback of his 28-fight career.
Buatsi Claims Victory in Uneventful Encounter
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of inactivity.
Earlier forecast as the next star of British boxing, he now finds himself trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors prepared to be aggressive in a calculated initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after damaging his hand during the bout, was making just his second appearance at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to narrowly win the more effective rounds.
The crowd's patience decreased because of constant clinching, with the challenger slipping to the canvas several times during close exchanges.
The underdog closed well, but many rounds were challenging to assess. Nevertheless, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, awarding Buatsi just one round.
Buatsi advances, but with the caliber of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Memorial Inspires Local Rivalry Contest
In the co-main event, Arthur defeated Rea by divided decision in a excellent all-Manchester fight to secure the European light heavyweight belt.
The stadium fell silent for a deeply poignant memorial before the fight as ten bells rang in memory of the city's native Hatton, who died aged 46 in September.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the final chime ended, the stillness transitioned to a chant of "there's just one Ricky Hatton".
The fighting during the bout matched the sentiment. The eventual winner was knocked down by a powerful punch squarely on the jaw in the early round, getting up unsteadily to his feet on the count of eight.
But the red-colored attire of Arthur soon came forward again. From the other corner, the opponent - in rival City blue - was injured quickly, significant bruising developing under his orbital area as the pair landed powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the action hardly diminished over the full distance.
Arthur barely secured the decision with scoring tallies of even score, close margin and 115-112, but each competitor were relentless and brave, all the qualities their hero Hatton embodied.
