British light-heavyweight Buatsi made a winning yet disappointing beginning to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a majority decision in a competitive ten-round bout at the boxing arena.
But Parker had his moments, landing some telling clean blows in a match where the styles didn't complement each other, with frequent clinching marring the fight.
Two judges scored it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my finest display but how do champions respond? They prevail," the victor stated in the ring as he was greeted with negative reactions from the crowd.
The British fighter got back to winning after his first professional defeat - an epic battle with Callum Smith in last winter - to secure a 20th pro success.
Various analysts felt Parker, 31, should have been awarded the win but the Derbyshire fighter endured the second setback of his 28-match professional journey.
The Champion Earns Triumph in Uneventful Match
The fighter's advancement has stalled in recent times through management issues and considerable time of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what seems like a last chance - under new promotional backing.
He opened tentatively, with both competitors prepared to overcommit in a calculated early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was participating in his second fight at light heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for the favorite, who utilized a tight guard to edge the more effective stanzas.
The crowd's patience decreased because of frequent holding, with Parker slipping to the canvas various instances during grappling.
The underdog closed well, but many rounds were hard to judge. However, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
The victor advances, but with the likes of hard hitter Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Homage Inspires Manchester Derby Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific Manchester vs Manchester battle to win the continental championship.
The arena fell silent for a profoundly moving homage before the fight as a bell ceremony sounded in remembrance of the city's native Ricky Hatton, who passed away at age 46 in September.
It was the premier televised boxing event in the city since Hatton's passing. As the last bell ended, the silence gave way to a chant of "only one Ricky Hatton".
The competition within the ring equaled the feeling. Arthur was floored by a left hook flush on the chin in the early round, standing uncertainly to his position on the eight count.
But the Manchester United-red shorts of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was marked up soon, significant bruising forming under his eye as the pair exchanged powerful shots.
Rea, 27, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the intensity seldom decreased over 12 rounds.
The victor barely secured the result with scoring tallies of even score, narrow lead and clearer margin, but each competitor were relentless and full of heart, all the qualities their hero the legend represented.
