British light heavyweight Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a close 10-round contest at the Manchester venue.
But the challenger landed significant shots, landing some telling individual punches in a contest where the approaches never quite clicked, with frequent clinching spoiling the action.
The scoring judges had it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They win," the victor said in the arena as he was met by boos from the spectators.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second defeat of his 28-match career.
Buatsi Claims Win in Dull Encounter
His career development has slowed in the past few years through management issues and considerable time of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to achieve expectations - maybe in what feels like a last chance - under fresh management.
He opened tentatively, with neither fighter prepared to take risks in a cagey opening few rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after breaking his hand during the bout, was competing in only his second appearance at light-heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who utilized a tight guard to edge the cleaner stanzas.
The audience's tolerance decreased amid regular grabbing, with Parker going down several times during clinches.
The underdog ended stronger, but several stanzas were challenging to assess. However, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Tribute Inspires Manchester Derby Fight
In the secondary fight, Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester contest to capture the European light-heavyweight belt.
The stadium fell silent for a profoundly moving tribute prior to the bout as a bell ceremony rang in remembrance of Manchester's own Hatton, who died 46 years old in last month.
It was the initial significant broadcast fight night in the city since Hatton's death. As the concluding sound ended, the silence transitioned to a chant of "there's just one Hatton".
The fighting within the ring reflected the emotion. Arthur was floored by a significant blow flush on the chin in the initial stage, standing uncertainly to his feet on the eight count.
But the red-colored attire of the fighter soon pressed ahead again. On the opposite side, Rea - in rival City blue - was marked up soon, heavy swelling developing under his face as the duo landed hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity rarely dropped over the full distance.
The victor barely secured the decision with judges scorecards of 114-114, narrow lead and wider gap, but the two athletes were determined and brave, exactly what their inspiration the legend embodied.
