British light heavyweight Buatsi secured a victory yet unimpressive start to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a tight ten-round fight at the Manchester venue.
But the challenger found success, delivering effective individual punches in a contest where the approaches never quite clicked, with frequent clinching disrupting the action.
The officials judged it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my greatest performance but what do champions do? They win," Buatsi stated in the ring as he was faced boos from the crowd.
The Londoner bounced back after his maiden career setback - an memorable fight with his previous opponent in last winter - to claim a twentieth professional win.
Various analysts thought the challenger, 31, deserved the win but the British boxer endured the second defeat of his 28-match career.
Buatsi Secures Victory in Dull Encounter
His career development has stalled in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to achieve expectations - maybe in what feels like a ultimate opportunity - under fresh management.
He started carefully, with both competitors prepared to take risks in a calculated opening few rounds.
Parker, 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 halfway stage, the underdog had kept it close, making life awkward for the favorite, who worked behind a solid defense to edge the better periods.
The crowd's patience wore thin because of regular grabbing, with the challenger slipping to the canvas several times during grappling.
Parker ended stronger, but many rounds were challenging to assess. However, ex-champion the boxing analyst - commentating on Dazn - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
The victor moves on, but with the likes of heavy hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Memorial Fuels Local Rivalry Contest
In the co-main event, Arthur defeated Rea by close verdict in a excellent all-Manchester battle to capture the European light heavyweight title.
The arena fell silent for a deeply poignant homage ahead of the contest as a bell ceremony tolled in memory of the city's native Ricky Hatton, who passed away aged 46 in last month.
It was the first major televised boxing event in the urban center since Hatton's passing. As the concluding sound ended, the stillness became a chant of "there's just one Hatton".
The action within the ring equaled the sentiment. Arthur was knocked down by a significant blow flush on the jaw in the second round, standing uncertainly to his position on the count of eight.
But the traditional red shorts of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was injured soon, heavy swelling forming under his eye as the pair traded hard punches.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the action rarely dropped over 12 rounds.
The victor barely secured the result with judges scorecards of even score, 115-113 and clearer margin, but the two athletes were relentless and full of heart, everything their inspiration the legend stood for.
