UK light heavyweight Buatsi earned a win yet disappointing start to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But the challenger found success, connecting with powerful clean blows in a fight where the approaches failed to mesh, with constant grabbing marring the fight.
The officials scored it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my finest display but how do champions respond? They win," the victor stated in the ringside as he was greeted with boos from the audience.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Various analysts thought the challenger, 31, deserved the decision but the contender experienced the second setback of his 28-bout career.
The Champion Earns Triumph in Dull Match
Buatsi's progress has plateaued in recent times through management issues and extended periods of lack of fights.
Once tipped as the rising talent of UK boxing, he now finds himself trying to achieve expectations - possibly in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with both competitors willing to overcommit in a calculated early stages.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second fight at the higher weight class.
By the fight's midpoint, Parker had made it competitive, making life awkward for the favorite, who operated with a tight guard to barely take the cleaner stanzas.
The crowd's patience diminished because of constant clinching, with the challenger falling to the floor multiple occasions during grappling.
The underdog ended stronger, but multiple periods were challenging to assess. However, previous titleholder Carl Frampton - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
Buatsi moves on, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Tribute Fuels All-Manchester Contest
In the supporting bout, Arthur overcame Bradley Rea by divided decision in a terrific local rivalry battle to secure the European light-heavyweight belt.
The venue became quiet for a deeply poignant memorial before the fight as a bell ceremony rang in remembrance of Manchester's own Ricky Hatton, who died at age 46 in recently.
It was the initial significant broadcast match card in the city since Hatton's passing. As the concluding sound faded, the silence gave way to a roar of "only one Ricky Hatton".
The fighting inside the ropes reflected the emotion. The eventual winner was floored by a significant blow squarely on the face in the second round, standing uncertainly to his feet on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, the opponent - in opposing blue - was damaged soon, significant bruising appearing under his orbital area as the duo traded powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the intensity hardly diminished over the full distance.
The victor barely secured the result with scoring tallies of draw, narrow lead and wider gap, but the two athletes were relentless and full of heart, all the qualities their idol the legend represented.
