UK light heavyweight Buatsi secured a victory yet unimpressive start to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a close ten-round bout at the Co-op Live Arena.
But Parker had his moments, connecting with powerful single shots in a contest where the techniques never quite clicked, with constant grabbing spoiling the contest.
Two judges had it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my finest display but how do champions respond? They succeed," Buatsi said in the arena as he was met by negative reactions from the crowd.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to claim a twentieth professional win.
Several boxing experts believed Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter endured the second setback of his 28-fight professional journey.
Buatsi Secures Win in Dull Affair
The fighter's advancement has slowed in recent times through management issues and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors willing to take risks in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was making just his second appearance at light heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for the favorite, who worked behind a tight guard to barely take the better rounds.
The crowd's patience decreased during regular grabbing, with the challenger going down various instances during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi advances, but with the caliber of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Hatton Tribute Inspires Manchester Derby Battle
In the supporting bout, Arthur beat Rea by divided decision in a terrific all-Manchester fight to win the European light heavyweight championship.
The stadium became quiet for a profoundly moving memorial before the fight as 10 bells sounded in honor of Manchester's own Hatton, who succumbed aged 46 in September.
It was the premier televised fight night in the urban center since the passing of Hatton. As the final chime disappeared, the quiet gave way to a roar of "there's only one Hatton".
The competition during the bout equaled the emotion. Arthur was floored by a left hook directly to the chin in the early 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 opposing blue - was injured early, heavy swelling developing under his eye as the duo landed powerful shots.
The challenger, 27, connected with strong blows but the champion, thirty-four, responded in kind with powerful upward punches as the pace hardly diminished over 12 rounds.
The victor edged the decision with scoring tallies of even score, close margin and clearer margin, but the two athletes were relentless and brave, exactly what their inspiration Hatton represented.
