UK light-heavyweight Buatsi made a winning yet disappointing start to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a competitive 10-round bout at the boxing arena.
But the challenger found success, connecting with powerful individual punches in a contest where the techniques failed to mesh, with constant grabbing spoiling the contest.
The officials had it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my best showing but what do champions do? They prevail," the victor commented in the ringside as he was met by negative reactions from the crowd.
The Londoner returned to winning ways after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a 20th pro success.
Some ringside observers believed Parker, 31, should have been awarded the decision but the Derbyshire fighter endured the second defeat of his 28-match career.
The Champion Secures Triumph in Slow Affair
Buatsi's progress has stalled in recent years through promotional disputes and considerable time of lack of fights.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with both competitors prepared to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was competing in only his second appearance at light heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a solid defense to narrowly win the more effective stanzas.
The audience's tolerance diminished amid constant clinching, with the challenger falling to the floor various instances during clinches.
Parker ended stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder the boxing analyst - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor advances, but with the likes of heavy hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Memorial Motivates Manchester Derby Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by split-decision in a outstanding Manchester vs Manchester fight to win the European light heavyweight title.
The arena grew hushed for a deeply poignant memorial ahead of the contest as a bell ceremony tolled in memory of local hero Ricky Hatton, who died 46 years old in recently.
It was the premier televised boxing event in the location since the passing of Hatton. As the last bell faded, the silence transitioned to a shout of "there's only one Hatton".
The competition within the ring reflected the emotion. Arthur was sent to the canvas by a significant blow squarely on the face in the initial stage, standing uncertainly to his feet on the referee's count.
But the Manchester United-red attire of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was marked up quickly, noticeable damage developing under his eye as the duo exchanged hard punches.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the action rarely dropped over the full distance.
The victor narrowly won the verdict with scoring tallies of draw, narrow lead and clearer margin, but the two athletes were relentless and brave, all the qualities their inspiration the legend represented.
