British light heavyweight Buatsi earned a win yet disappointing beginning to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a majority decision in a close ten-round fight at the boxing arena.
But the challenger had his moments, delivering effective clean blows in a match where the approaches didn't complement each other, with frequent clinching spoiling the contest.
The officials scored it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my greatest display but what do champions do? They win," the victor commented in the arena as he was greeted with disapproval from the audience.
The Londoner bounced back after his first professional defeat - an epic battle with his previous opponent in last winter - to claim a 20th pro success.
Various analysts felt the challenger, thirty-one, merited the decision but the Derbyshire fighter suffered the second loss of his 28-fight career.
The Champion Secures Triumph in Dull Match
His career development has plateaued in recent years through contract problems and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to fulfil that early promise - possibly in what feels like a last chance - under recent support.
He opened tentatively, with neither fighter ready to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second bout at light heavyweight.
By the middle rounds, the underdog had kept it close, causing problems for Buatsi, who worked behind a solid defense to barely take the more effective stanzas.
The audience's tolerance wore thin amid frequent holding, with the challenger going down multiple occasions during grappling.
Parker ended stronger, but several stanzas were difficult to score. However, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
The victor moves on, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Memorial Inspires All-Manchester Fight
In the supporting bout, Arthur beat Rea by divided decision in a excellent Manchester vs Manchester fight to win the continental championship.
The arena became quiet for a deeply poignant memorial ahead of the contest as a bell ceremony rang in remembrance of Manchester's own Hatton, who died at age 46 in last month.
It was the first major televised match card in the city since the passing of Hatton. As the final chime faded, the stillness transitioned to a roar of "there's only one Ricky Hatton".
The action inside the ropes matched the sentiment. The eventual winner was knocked down by a significant blow flush on the face in the initial stage, getting up unsteadily to his position on the eight count.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, Rea - in competitive blue - was injured soon, noticeable damage developing under his orbital area as the duo exchanged hard punches.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with effective uppercuts as the intensity seldom decreased over the full distance.
The victor edged the decision with official scores of 114-114, close margin and wider gap, but both fighters were relentless and courageous, exactly what their idol Hatton embodied.
