UK light heavyweight Buatsi earned a win yet disappointing start to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a tight ten-round bout at the Co-op Live Arena.
But the challenger found success, delivering effective single shots in a contest where the techniques didn't complement each other, with frequent clinching spoiling the action.
Two judges had it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest display but what defines champions? They prevail," Buatsi said in the ringside as he was faced disapproval from the crowd.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Several boxing experts believed the challenger, thirty-one, deserved the victory but the contender experienced the second loss of his 28-match professional journey.
Buatsi Claims Victory in Slow Affair
Buatsi's progress has slowed in recent years through management issues and extended periods of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with the two boxers prepared to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for the favorite, who operated with a tight guard to edge the better stanzas.
The audience's tolerance decreased amid frequent holding, with the challenger going down multiple occasions during close exchanges.
The underdog closed well, but several stanzas were difficult to score. Nevertheless, former world champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - based on this performance - still looks steep.
Hatton Homage Motivates All-Manchester Contest
In the co-main event, Arthur overcame Bradley Rea by close verdict in a outstanding local rivalry fight to capture the European light heavyweight belt.
The venue grew hushed for a deeply poignant tribute before the fight as ten bells rang in remembrance of local hero Ricky Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the last bell faded, the stillness gave way to a shout of "there's only one Ricky Hatton".
The action within the ring reflected the sentiment. The eventual winner was floored by a significant blow flush on the face in the second round, getting up unsteadily to his feet on the count of eight.
But the red-colored equipment of Arthur soon came forward again. Across the ring, Rea - in opposing blue - was damaged soon, heavy swelling forming under his face as the pair exchanged punishing blows.
The challenger, 27, connected with strong blows but the champion, 34, fought fire with fire with effective uppercuts as the pace hardly diminished over twelve rounds.
The victor barely secured the result with official scores of 114-114, narrow lead and 115-112, but both fighters were persistent and courageous, exactly what their idol the legend stood for.
