British light-heavyweight Buatsi secured a victory yet unimpressive beginning to his career under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a competitive ten-round bout at the Co-op Live Arena.
But Parker landed significant shots, delivering effective clean blows in a match where the approaches failed to mesh, with excessive holding spoiling the action.
The officials had it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my best display but what defines champions? They win," Buatsi stated in the arena as he was faced negative reactions from the spectators.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Several boxing experts believed the challenger, thirty-one, should have been awarded the decision but the contender experienced the second defeat of his 28-match professional journey.
Buatsi Secures Victory in Dull Affair
Buatsi's progress has slowed in the past few years through contract problems and considerable time of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - possibly in what feels like a ultimate opportunity - under recent support.
He started carefully, with both competitors ready to be aggressive in a calculated early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand in the contest, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a protective stance to narrowly win the better rounds.
The spectators' acceptance wore thin amid constant clinching, with the challenger going down multiple occasions during grappling.
Parker ended stronger, but multiple periods were challenging to assess. Although, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of power puncher Benavidez, and Russian star Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Hatton Memorial Fuels Local Rivalry Contest
In the secondary fight, Arthur beat Rea by split-decision in a terrific all-Manchester contest to secure the European light heavyweight championship.
The venue became quiet for a deeply poignant memorial ahead of the contest as 10 bells tolled in honor of Manchester's own Hatton, who died 46 years old in recently.
It was the premier televised match card in the location since Hatton's death. As the final chime disappeared, the silence became a roar of "only one Hatton".
The action within the ring matched the emotion. The eventual winner was knocked down by a left hook flush on the face in the early round, getting up unsteadily to his position on the count of eight.
But the red-colored attire of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was injured early, noticeable damage appearing under his face as the duo exchanged hard punches.
The challenger, 27, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the pace hardly diminished over the full distance.
The victor edged the decision with judges scorecards of 114-114, 115-113 and clearer margin, but the two athletes were relentless and brave, everything their idol the legend embodied.
