British light-heavyweight Buatsi made a winning yet disappointing beginning to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a competitive ten-round bout at the Manchester venue.
But the challenger landed significant shots, landing some telling single shots in a contest where the styles failed to mesh, with excessive holding marring the contest.
The officials scored it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my finest performance but what do champions do? They prevail," the victor stated in the ring as he was faced boos from the spectators.
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 pro success.
Various analysts believed Parker, thirty-one, deserved the decision but the contender suffered the second defeat of his 28-fight professional journey.
The Champion Earns Win in Dull Encounter
The fighter's advancement has stalled in recent times through contract problems and considerable time of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to fulfil that early promise - maybe in what appears to be a last chance - under new promotional backing.
He started carefully, with neither fighter willing to be aggressive in a cagey initial rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was competing in only his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who utilized a tight guard to narrowly win the cleaner rounds.
The spectators' acceptance diminished during regular grabbing, with Parker slipping to the canvas various instances during close exchanges.
Parker finished the stronger, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
Buatsi progresses, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Memorial Inspires All-Manchester Battle
In the secondary fight, Lyndon Arthur defeated Rea by split-decision in a terrific local rivalry contest to capture the European light heavyweight title.
The arena became quiet for a deeply poignant homage ahead of the contest as ten bells tolled in honor of local hero Hatton, who succumbed 46 years old in September.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the concluding sound faded, the silence transitioned to a chant of "only one Ricky Hatton".
The fighting inside the ropes equaled the feeling. Arthur was knocked down by a powerful punch squarely on the face in the second round, standing uncertainly to his footing on the eight count.
But the traditional red attire of Arthur soon came forward again. Across the ring, the opponent - in rival City blue - was damaged quickly, heavy swelling developing under his orbital area as the pair traded powerful shots.
Rea, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace seldom decreased over 12 rounds.
The victor barely secured the result with official scores of draw, narrow lead and 115-112, but the two athletes were relentless and courageous, everything their idol Hatton embodied.
