UK light heavyweight Buatsi made a winning yet underwhelming beginning to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a close ten-round fight at the boxing arena.
But Parker had his moments, delivering effective individual punches in a contest where the approaches failed to mesh, with constant grabbing marring the fight.
The officials had it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest performance but what defines champions? They prevail," Buatsi said in the ring as he was faced disapproval from the audience.
The Londoner returned to winning ways after his initial pro loss - an epic battle with Callum Smith in last winter - to secure a 20th pro success.
Several boxing experts thought Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second loss of his 28-bout career.
Buatsi Claims Win in Slow Encounter
The fighter's advancement has plateaued in recent years through management issues and considerable time of lack of fights.
Once tipped as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors prepared to take risks in a tentative early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second fight at light-heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for Buatsi, who operated with a tight guard to narrowly win the more effective stanzas.
The audience's tolerance decreased during regular grabbing, with Parker falling to the floor several times during close exchanges.
The underdog ended stronger, but many rounds were difficult to score. However, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, giving Buatsi just only one stanza.
The victor advances, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Hatton Memorial Fuels Manchester Derby Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding Manchester vs Manchester battle to capture the continental championship.
The arena fell silent for a deeply poignant homage ahead of the contest as 10 bells rang in memory of Manchester's own Hatton, who passed away 46 years old in September.
It was the premier televised fight night in the location since Hatton's death. As the last bell ended, the quiet became a roar of "there's only one Ricky Hatton".
The fighting inside the ropes matched the feeling. The eventual winner was knocked down by a significant blow directly to the jaw in the early round, getting up unsteadily to his feet on the eight count.
But the red-colored equipment of the fighter soon pressed ahead again. Across the ring, the opponent - in opposing blue - was marked up quickly, significant bruising developing under his face as the duo landed hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action hardly diminished over the full distance.
The victor narrowly won the verdict with official scores of 114-114, narrow lead and clearer margin, but the two athletes were persistent and full of heart, everything their inspiration the legend stood for.
