British light heavyweight Buatsi secured a victory yet underwhelming debut to his career under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a tight 10-round contest at the boxing arena.
But the challenger had his moments, landing some telling individual punches in a fight where the styles failed to mesh, with excessive holding marring the fight.
The scoring judges judged it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest display but how do champions respond? They win," the victor commented in the ringside as he was met by boos from the spectators.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Several boxing experts believed Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter endured the second setback of his 28-bout professional journey.
Buatsi Claims Triumph in Slow Affair
His career development has stalled in the past few years through management issues and considerable time of lack of fights.
Previously predicted as the next star of UK boxing, he now stands trying to fulfil that early promise - possibly in what appears to be a last chance - under recent support.
He began cautiously, with both competitors willing to be aggressive in a tentative early stages.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the middle rounds, Parker had made it competitive, making life awkward for the favorite, who worked behind a tight guard to edge the better stanzas.
The spectators' acceptance diminished during regular grabbing, with Parker slipping to the canvas various instances during grappling.
The underdog finished the stronger, but several stanzas were difficult to score. Although, previous titleholder the boxing analyst - working with Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
Buatsi progresses, but with the caliber of hard hitter David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Hatton Memorial Fuels All-Manchester Fight
In the secondary fight, Arthur beat Bradley Rea by close verdict in a excellent local rivalry fight to win the European light-heavyweight belt.
The arena grew hushed for a extremely emotional tribute before the fight as a bell ceremony tolled in remembrance of local hero Ricky Hatton, who passed away 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 disappeared, the silence gave way to a roar of "there's just one Hatton".
The competition during the bout equaled the emotion. The eventual winner was knocked down by a powerful punch squarely on the face in the early round, rising shakily to his position on the eight count.
But the Manchester United-red equipment of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was damaged quickly, noticeable damage forming under his eye as the fighters landed hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with effective uppercuts as the action hardly diminished over the full distance.
Arthur edged the result with judges scorecards of 114-114, close margin and 115-112, but the two athletes were relentless and full of heart, exactly what their idol the legend represented.
