British light-heavyweight Buatsi earned a win yet underwhelming start to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive ten-round fight at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful individual punches in a match where the approaches never quite clicked, with excessive holding spoiling the fight.
Two judges had it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my best display but what do champions do? They win," the victor stated in the ring as he was met by boos from the spectators.
The Londoner bounced back after his maiden career setback - an memorable fight with his previous opponent in last winter - to earn a 20th pro success.
Various analysts felt the challenger, 31, should have been awarded the victory but the British boxer experienced the second setback of his 28-match professional journey.
Buatsi Earns Win in Uneventful Match
His career development has slowed in recent years through contract problems and considerable time of inactivity.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter willing to take risks in a cagey initial rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was competing in only his second fight at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for Buatsi, who utilized a solid defense to edge the cleaner periods.
The audience's tolerance diminished because of constant clinching, with Parker slipping to the canvas multiple occasions during close exchanges.
Parker closed well, but many rounds were challenging to assess. Although, previous titleholder Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, giving Buatsi just a single round.
Buatsi advances, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still seems difficult.
Hatton Tribute Fuels Local Rivalry Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by split-decision in a outstanding Manchester vs Manchester fight to secure the continental belt.
The venue grew hushed for a deeply poignant memorial prior to the bout as a bell ceremony tolled in honor of Manchester's own Hatton, who died 46 years old in recently.
It was the premier televised match card in the city since the passing of Hatton. As the last bell faded, the quiet gave way to a roar of "there's only one Hatton".
The action within the ring equaled the emotion. The eventual winner was sent to the canvas by a left hook flush on the chin in the initial stage, rising shakily to his footing on the eight count.
But the red-colored attire of the fighter soon came forward again. On the opposite side, the opponent - in rival City blue - was damaged early, significant bruising forming under his face as the fighters landed punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity rarely dropped over twelve rounds.
The victor barely secured the verdict with official scores of 114-114, narrow lead and 115-112, but the two athletes were persistent and brave, all the qualities their idol the legend embodied.
