UK light heavyweight Buatsi secured a victory yet unimpressive debut to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a competitive ten-round contest at the Manchester venue.
But Parker found success, landing some telling clean blows in a match where the approaches never quite clicked, with excessive holding disrupting the fight.
Two judges had it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my greatest performance but what defines champions? They succeed," the victor commented in the arena as he was met by negative reactions from the audience.
The Londoner returned to winning ways after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Various analysts felt the challenger, thirty-one, deserved the decision but the Derbyshire fighter endured the second loss of his 28-match professional journey.
The Champion Secures Win in Dull Match
Buatsi's progress has stalled in recent years through management issues and extended periods of inactivity.
Previously predicted as the next star of British boxing, he now is positioned trying to achieve expectations - maybe in what seems like a last chance - under new promotional backing.
He started carefully, with the two boxers willing to take risks in a tentative early stages.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was competing in only his second appearance at light-heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for Buatsi, who operated with a protective stance to narrowly win the more effective stanzas.
The audience's tolerance decreased because of regular grabbing, with the challenger going down several times during clinches.
The underdog ended stronger, but several stanzas were hard to judge. However, previous titleholder Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
The victor advances, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Tribute Motivates Local Rivalry Fight
In the supporting bout, Lyndon Arthur defeated Rea by split-decision in a excellent all-Manchester battle to win the European light heavyweight championship.
The venue fell silent for a deeply poignant memorial ahead of the contest as a bell ceremony tolled in remembrance of the city's native Ricky Hatton, who died at age 46 in last month.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the concluding sound ended, the silence gave way to a roar of "there's only one Hatton".
The fighting during the bout matched the emotion. The eventual winner was sent to the canvas by a left hook flush on the face in the initial stage, standing uncertainly to his position on the count of eight.
But the red-colored shorts of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was marked up soon, noticeable damage appearing under his face as the pair exchanged punishing blows.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the pace rarely dropped over the full distance.
Arthur edged the decision with official scores of 114-114, 115-113 and 115-112, but each competitor were determined and courageous, exactly what their idol Hatton stood for.
