British light-heavyweight Buatsi made a winning yet unimpressive beginning to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a tight ten-round bout at the boxing arena.
But the challenger landed significant shots, landing some telling single shots in a match where the techniques failed to mesh, with excessive holding marring the contest.
The officials had it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my best display but what defines champions? They win," Buatsi said in the ringside as he was faced negative reactions from the audience.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to claim a 20th career victory.
Some ringside observers felt Parker, thirty-one, merited the win but the British boxer suffered the second loss of his 28-match professional journey.
Buatsi Earns Victory in Slow Affair
The fighter's advancement has slowed in the past few years through contract problems and considerable time of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to realize his potential - maybe in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with the two boxers ready to take risks in a cagey initial rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second fight at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for Buatsi, who utilized a protective stance to edge the better stanzas.
The spectators' acceptance wore thin because of regular grabbing, with the challenger falling to the floor several times during grappling.
Parker closed well, but multiple periods were hard to judge. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the likes of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Tribute Fuels Manchester Derby Battle
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a excellent Manchester vs Manchester battle to win the European light heavyweight title.
The venue fell silent for a profoundly moving memorial prior to the bout as a bell ceremony sounded in memory of the city's native Ricky Hatton, who died aged 46 in September.
It was the premier televised fight night in the location since Hatton's death. As the concluding sound faded, the silence transitioned to a chant of "only one Ricky Hatton".
The fighting inside the ropes reflected the emotion. The eventual winner was sent to the canvas by a significant blow squarely on the face in the second round, rising shakily to his footing on the eight count.
But the red-colored attire of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was marked up soon, noticeable damage developing under his face as the fighters landed hard punches.
Rea, 27, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the intensity rarely dropped over 12 rounds.
The victor edged the verdict with official scores of 114-114, narrow lead and clearer margin, but both fighters were relentless and brave, all the qualities their inspiration the legend represented.
