UK light heavyweight Buatsi earned a win yet underwhelming start to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a judges' verdict in a tight 10-round contest at the boxing arena.
But the challenger had his moments, delivering effective single shots in a fight where the approaches didn't complement each other, with excessive holding marring the action.
Two judges scored it 96-94 for to the winner, with the third a 95-95.
"It wasn't my finest showing but what do champions do? They win," the victor commented in the ringside as he was greeted with disapproval from the crowd.
The British fighter returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to earn a 20th career victory.
Several boxing experts felt Parker, thirty-one, deserved the decision but the contender experienced the second setback of his 28-bout professional journey.
Buatsi Claims Triumph in Dull Encounter
Buatsi's progress has stalled in the past few years through promotional disputes and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now stands trying to achieve expectations - possibly in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter ready to be aggressive in a calculated initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second fight at light heavyweight.
By the halfway stage, Parker had stayed in contention, making life awkward for the favorite, who utilized a protective stance to narrowly win the cleaner rounds.
The audience's tolerance diminished because of frequent holding, with the challenger slipping to the canvas several times during clinches.
Parker ended stronger, but many rounds were challenging to assess. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, awarding Buatsi just one round.
Buatsi progresses, but with the presence of power puncher David Benavidez, and Russian champion Bivol ruling the division, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Memorial Inspires Manchester Derby Battle
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a outstanding all-Manchester contest to win the European light heavyweight belt.
The venue grew hushed for a extremely emotional memorial before the fight as a bell ceremony rang in honor of local hero Ricky Hatton, who died 46 years old in September.
It was the initial significant broadcast match card in the urban center since the passing of Hatton. As the concluding sound ended, the quiet became a chant of "only one Ricky Hatton".
The competition during the bout reflected the sentiment. The eventual winner was sent to the canvas by a powerful punch directly to the face in the initial stage, getting up unsteadily to his position on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was marked up quickly, significant bruising forming under his eye as the fighters exchanged powerful shots.
Rea, 27, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the action hardly diminished over the full distance.
The victor narrowly won the decision with official scores of even score, narrow lead and 115-112, but the two athletes were determined and full of heart, all the qualities their inspiration the legend represented.
