UK light-heavyweight Buatsi secured a victory yet underwhelming debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive 10-round bout at the boxing arena.
But Parker had his moments, landing some telling individual punches in a contest where the techniques failed to mesh, with excessive holding 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 display but how do champions respond? They prevail," Buatsi said in the arena as he was faced negative reactions from the spectators.
The Londoner bounced back after his first professional defeat - an thrilling contest with Callum Smith in February - to earn a twentieth professional win.
Several boxing experts thought the challenger, 31, deserved the win but the Derbyshire fighter experienced the second defeat of his 28-bout professional journey.
Buatsi Claims Win in Dull Affair
The fighter's advancement has slowed in recent times through promotional disputes and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under recent support.
He started carefully, with neither fighter willing to take risks in a tentative initial rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after breaking his hand in the contest, was competing in only his second fight at the higher weight class.
By the halfway stage, the underdog had made it competitive, causing problems for the favorite, who utilized a protective stance to barely take the better periods.
The spectators' acceptance diminished amid frequent holding, with the challenger slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but several stanzas were difficult to score. Although, previous titleholder the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just one round.
Buatsi advances, but with the presence 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 Tribute Motivates Local Rivalry Contest
In the supporting bout, Arthur beat Bradley Rea by divided decision in a terrific local rivalry contest to secure the European light heavyweight title.
The stadium grew hushed for a extremely emotional memorial prior to the bout as a bell ceremony tolled in memory of local hero Hatton, who passed away 46 years old in last month.
It was the first major televised boxing event in the city since the passing of Hatton. As the final chime ended, the silence gave way to a roar of "there's just one Hatton".
The competition during the bout matched the emotion. The eventual winner was sent to the canvas by a powerful punch flush on the chin in the early round, rising shakily to his footing on the count of eight.
But the red-colored attire of the fighter soon pressed ahead again. Across the ring, Rea - in rival City blue - was marked up soon, heavy swelling appearing under his orbital area as the fighters landed powerful shots.
The challenger, 27, landed power punches but Arthur, thirty-four, matched the intensity with powerful upward punches as the intensity rarely dropped over 12 rounds.
The victor edged the verdict with official scores of even score, narrow lead and clearer margin, but each competitor were persistent and full of heart, exactly what their hero the legend stood for.
