UK light heavyweight Buatsi earned a win yet underwhelming debut to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a majority decision in a competitive 10-round contest at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a match where the approaches never quite clicked, with frequent clinching spoiling the contest.
The officials judged it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my finest performance but what defines champions? They succeed," Buatsi stated in the ring as he was faced negative reactions from the spectators.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Various analysts believed Parker, thirty-one, deserved the decision but the Derbyshire fighter suffered the second setback of his 28-fight career.
Buatsi Earns Triumph in Slow Encounter
The fighter's advancement has stalled in recent years through promotional disputes and long spells of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what feels like a ultimate opportunity - under fresh management.
He started carefully, with neither fighter prepared to take risks in a tentative early stages.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second fight at light heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who utilized a protective stance to edge the more effective rounds.
The spectators' acceptance wore thin during frequent holding, with Parker falling to the floor multiple occasions during grappling.
The underdog finished the stronger, but many rounds were hard to judge. However, former world champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Tribute Fuels All-Manchester Battle
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a terrific Manchester vs Manchester fight to win the European light heavyweight championship.
The arena became quiet for a profoundly moving tribute ahead of the contest as 10 bells tolled in memory of the city's native Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the concluding sound faded, the silence transitioned to a roar of "there's only one Hatton".
The action within the ring equaled the emotion. The eventual winner was knocked down by a powerful punch directly to the face in the early round, standing uncertainly to his feet on the eight count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was marked up quickly, heavy swelling developing under his face as the fighters exchanged powerful shots.
Rea, 27, landed power punches but the champion, 34, responded in kind with effective uppercuts as the pace hardly diminished over 12 rounds.
Arthur barely secured the verdict with scoring tallies of draw, close margin and clearer margin, but both fighters were relentless and brave, all the qualities their hero Hatton stood for.
