British light heavyweight Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a tight ten-round bout at the Manchester venue.
But the challenger found success, landing some telling single shots in a match where the styles never quite clicked, with excessive holding marring the fight.
Two judges had it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my best display but how do champions respond? They prevail," Buatsi commented in the ring as he was faced negative reactions from the audience.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Various analysts believed the challenger, 31, merited the win but the contender suffered the second loss of his 28-match career.
The Champion Claims Victory in Dull Match
His career development has slowed in the past few years through management issues and extended periods of lack of fights.
Once tipped as the next star of the British fight scene, he now stands trying to fulfil that early promise - maybe in what appears to be a last chance - under recent support.
He began cautiously, with both competitors willing to overcommit in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who worked behind a tight guard to edge the better stanzas.
The crowd's patience decreased amid frequent holding, with Parker falling to the floor various instances during close exchanges.
Parker finished the stronger, but multiple periods were hard to judge. Nevertheless, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still appears challenging.
Hatton Tribute Motivates Manchester Derby Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by split-decision in a terrific all-Manchester fight to win the continental title.
The venue fell silent for a deeply poignant tribute prior to the bout as 10 bells tolled in memory of local hero Ricky Hatton, who passed away at age 46 in September.
It was the premier televised fight night in the city since Hatton's passing. As the last bell disappeared, the silence transitioned to a roar of "only one Ricky Hatton".
The fighting during the bout equaled the feeling. Arthur was floored by a powerful punch directly to the face in the early round, getting up unsteadily to his feet on the eight count.
But the traditional red attire of Arthur soon pressed ahead again. From the other corner, Rea - in opposing blue - was damaged early, noticeable damage appearing under his face as the pair landed hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with effective uppercuts as the pace hardly diminished over twelve rounds.
The victor narrowly won the decision with judges scorecards of 114-114, close margin and 115-112, but each competitor were persistent and courageous, everything their idol Hatton stood for.
