UK light-heavyweight Buatsi secured a victory yet disappointing debut to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a competitive 10-round contest at the Co-op Live Arena.
But Parker landed significant shots, landing some telling clean blows in a fight where the techniques never quite clicked, with excessive holding marring the fight.
The scoring judges had it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my best showing but what do champions do? They prevail," the victor stated in the ringside as he was met by negative reactions from the spectators.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in February - to earn a twentieth professional win.
Some ringside observers thought Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter experienced the second loss of his 28-bout career.
The Champion Secures Win in Dull Affair
His career development has stalled in recent times through contract problems and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now finds himself trying to realize his potential - perhaps in what feels like a last chance - under fresh management.
He opened tentatively, with neither fighter ready to be aggressive in a tentative initial rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after damaging his hand during the bout, was competing in only his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a solid defense to narrowly win the cleaner stanzas.
The audience's tolerance decreased during frequent holding, with Parker slipping to the canvas several times during grappling.
The underdog ended stronger, but multiple periods were challenging to assess. Although, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, giving Buatsi just one round.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Homage Motivates Local Rivalry Contest
In the supporting bout, Arthur defeated Bradley Rea by close verdict in a excellent all-Manchester battle to secure the European light-heavyweight title.
The stadium became quiet for a extremely emotional memorial ahead of the contest as 10 bells rang in honor of local hero Hatton, who passed away 46 years old in last month.
It was the first major televised fight night in the city since Hatton's death. As the concluding sound faded, the stillness became a roar of "only one Ricky Hatton".
The fighting inside the ropes equaled the emotion. The eventual winner was knocked down by a powerful punch directly to the chin in the early round, standing uncertainly to his position on the referee's count.
But the Manchester United-red attire of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was marked up soon, noticeable damage developing under his eye as the fighters landed powerful shots.
Rea, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the pace hardly diminished over twelve rounds.
Arthur edged the verdict with official scores of draw, close margin and 115-112, but each competitor were determined and full of heart, exactly what their idol the legend represented.
