UK light-heavyweight Buatsi made a winning yet underwhelming beginning to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a close ten-round contest at the Co-op Live Arena.
But Parker found success, landing some telling individual punches in a fight where the techniques failed to mesh, with frequent clinching marring the action.
The officials had it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest showing but what defines champions? They succeed," Buatsi commented in the arena as he was faced boos from the spectators.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Several boxing experts felt the challenger, thirty-one, merited the decision but the Derbyshire fighter suffered the second setback of his 28-bout career.
Buatsi Earns Triumph in Uneventful Encounter
Buatsi's progress has plateaued in recent times through promotional disputes and long spells of inactivity.
Previously predicted as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter prepared to be aggressive in a tentative initial rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand during the bout, was participating in his second fight at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for the favorite, who operated with a protective stance to edge the cleaner periods.
The spectators' acceptance diminished during constant clinching, with Parker slipping to the canvas several times during grappling.
The underdog closed well, but several stanzas were difficult to score. Nevertheless, former world champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the presence of hard hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Hatton Homage Motivates All-Manchester Contest
In the co-main event, Lyndon Arthur beat Rea by split-decision in a excellent Manchester vs Manchester fight to capture the continental championship.
The stadium became quiet for a profoundly moving memorial prior to the bout as a bell ceremony sounded in memory of Manchester's own Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the last bell disappeared, the stillness transitioned to a roar of "there's only one Hatton".
The competition within the ring matched the feeling. The eventual winner was floored by a left hook directly to the chin in the second round, getting up unsteadily to his feet on the referee's count.
But the traditional red equipment of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was injured soon, heavy swelling developing under his eye as the duo traded hard punches.
The challenger, 27, landed power punches but Arthur, thirty-four, matched the intensity with stinging uppercuts as the action seldom decreased over 12 rounds.
Arthur barely secured the verdict with judges scorecards of 114-114, narrow lead and wider gap, but the two athletes were persistent and brave, exactly what their inspiration Hatton embodied.
