British light-heavyweight Buatsi secured a victory yet disappointing beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a tight ten-round bout at the Co-op Live Arena.
But Parker found success, connecting with powerful individual punches in a contest where the styles didn't complement each other, with constant grabbing spoiling the contest.
The officials judged it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my best showing but how do champions respond? They prevail," the victor commented in the arena as he was greeted with disapproval from the audience.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Various analysts felt the challenger, thirty-one, deserved the victory but the Derbyshire fighter experienced the second setback of his 28-bout professional journey.
The Champion Secures Triumph in Uneventful Encounter
His career development has plateaued in recent years through management issues and long spells of inactivity.
Once tipped as the rising talent of British boxing, he now stands trying to fulfil that early promise - possibly in what appears to be a last chance - under fresh management.
He opened tentatively, with the two boxers ready to take risks in a calculated initial 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 in the contest, was participating in his second appearance at the higher weight class.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who operated with a solid defense to barely take the more effective stanzas.
The audience's tolerance wore thin amid regular grabbing, with Parker going down multiple occasions during close exchanges.
Parker closed well, but several stanzas were challenging to assess. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just one round.
The victor advances, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Hatton Tribute Motivates Manchester Derby Contest
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding local rivalry contest to win the European light heavyweight belt.
The arena became quiet for a deeply poignant memorial prior to the bout as a bell ceremony sounded in remembrance of Manchester's own Hatton, who succumbed at age 46 in September.
It was the first major televised boxing event in the city since Hatton's death. As the final chime disappeared, the silence became a shout of "there's just one Hatton".
The action during the bout equaled the sentiment. Arthur was knocked down by a left hook directly to the chin in the early round, getting up unsteadily to his footing on the eight count.
But the traditional red shorts of the fighter soon came forward again. Across the ring, the opponent - in rival City blue - was injured quickly, noticeable damage developing under his orbital area as the duo landed hard punches.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor narrowly won the verdict with judges scorecards of 114-114, narrow lead and 115-112, but the two athletes were persistent and full of heart, all the qualities their idol Hatton represented.
