British light heavyweight Buatsi made a winning yet unimpressive beginning to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a majority decision in a close 10-round bout at the Manchester venue.
But the challenger landed significant shots, connecting with powerful single shots in a contest where the approaches never quite clicked, with constant grabbing marring the contest.
The officials had it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what do champions do? They win," Buatsi said in the arena as he was faced negative reactions from the spectators.
The British fighter bounced back after his initial pro loss - an epic battle with Callum Smith in last winter - to earn a 20th career victory.
Some ringside observers thought the challenger, 31, deserved the victory but the Derbyshire fighter suffered the second defeat of his 28-match career.
Buatsi Claims Win in Dull Match
Buatsi's progress has slowed in recent times through management issues and long spells of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to realize his potential - possibly in what feels like a last chance - under recent support.
He began cautiously, with both competitors prepared to be aggressive in a cagey early stages.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was competing in only his second appearance at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a protective stance to narrowly win the more effective stanzas.
The audience's tolerance decreased during frequent holding, with the challenger slipping to the canvas various instances during clinches.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
Buatsi moves on, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Memorial Fuels Local Rivalry Contest
In the co-main event, Arthur beat Rea by split-decision in a excellent Manchester vs Manchester contest to secure the European light heavyweight belt.
The venue grew hushed for a profoundly moving tribute ahead of the contest as a bell ceremony tolled in memory of the city's native Ricky Hatton, who succumbed at age 46 in last month.
It was the premier televised match card in the location since Hatton's death. As the last bell faded, the quiet became a chant of "only one Ricky Hatton".
The action inside the ropes matched the emotion. Arthur was knocked down by a significant blow flush on the chin in the second round, standing uncertainly to his footing on the eight count.
But the red-colored attire of Arthur soon advanced again. Across the ring, Rea - in competitive blue - was injured quickly, noticeable damage forming under his orbital area as the fighters traded powerful shots.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the intensity rarely dropped over 12 rounds.
Arthur edged the result with scoring tallies of 114-114, close margin and clearer margin, but each competitor were persistent and courageous, everything their hero the legend represented.
