British light heavyweight Buatsi secured a victory yet underwhelming debut to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a judges' verdict in a close ten-round bout at the Co-op Live Arena.
But the challenger had his moments, landing some telling single shots in a fight where the techniques failed to mesh, with frequent clinching marring the action.
Two judges judged it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my best showing but what defines champions? They prevail," the victor commented in the ringside as he was faced boos from the spectators.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to claim a 20th career victory.
Some ringside observers believed Parker, 31, should have been awarded the decision but the British boxer endured the second setback of his 28-bout career.
The Champion Earns Triumph in Slow Affair
Buatsi's progress has slowed in the past few years through contract problems and long spells of lack of fights.
Earlier forecast as the future of British boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a last chance - under new promotional backing.
He began cautiously, with the two boxers ready to be aggressive in a tentative opening few rounds.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was making just his second bout at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a protective stance to narrowly win the better periods.
The crowd's patience decreased during regular grabbing, with the challenger falling to the floor various instances during grappling.
Parker closed well, but many rounds were hard to judge. Although, ex-champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi advances, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Tribute Inspires Manchester Derby Contest
In the co-main event, Arthur defeated Bradley Rea by close verdict in a excellent Manchester vs Manchester fight to win the European light heavyweight belt.
The venue fell silent for a profoundly moving homage ahead of the contest as ten bells rang in memory of the city's native Hatton, who succumbed 46 years old in recently.
It was the first major televised match card in the urban center since Hatton's passing. As the concluding sound disappeared, the quiet transitioned to a shout of "there's only one Ricky Hatton".
The competition during the bout equaled the sentiment. Arthur was sent to the canvas by a significant blow directly to the face in the early round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in opposing blue - was damaged soon, significant bruising developing under his face as the pair exchanged punishing blows.
Rea, 27, connected with strong blows but the champion, thirty-four, responded in kind with stinging uppercuts as the action seldom decreased over twelve rounds.
Arthur narrowly won the result with official scores of 114-114, 115-113 and 115-112, but both fighters were persistent and brave, all the qualities their hero the legend embodied.
