British light heavyweight Buatsi earned a win yet underwhelming beginning to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a majority decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling individual punches in a fight where the approaches never quite clicked, with frequent clinching marring the action.
Two judges judged it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best performance but what defines champions? They prevail," Buatsi stated in the ringside as he was greeted with disapproval from the audience.
The British fighter bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, deserved the win but the Derbyshire fighter experienced the second setback of his 28-match career.
Buatsi Claims Victory in Dull Match
Buatsi's progress has stalled in the past few years through contract problems and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now is positioned trying to achieve expectations - possibly in what seems like a ultimate opportunity - under recent support.
He started carefully, with the two boxers ready to take risks in a calculated early stages.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was making just his second bout at light heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for Buatsi, who worked behind a protective stance to edge the better rounds.
The audience's tolerance wore thin during constant clinching, with Parker going down multiple occasions during clinches.
Parker finished the stronger, but multiple periods were hard to judge. However, former world champion the boxing analyst - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the presence of hard hitter Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Hatton Memorial Inspires All-Manchester Battle
In the co-main event, Lyndon Arthur overcame Rea by divided decision in a excellent Manchester vs Manchester fight to win the continental championship.
The stadium fell silent for a extremely emotional tribute ahead of the contest as a bell ceremony tolled in memory of the city's native Ricky Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast match card in the location since Hatton's passing. As the concluding sound ended, the silence became a roar of "there's just one Hatton".
The action within the ring matched the feeling. Arthur was sent to the canvas by a left hook flush on the face in the second round, rising shakily to his feet on the referee's count.
But the red-colored attire of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was marked up soon, noticeable damage appearing under his eye as the fighters exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with stinging uppercuts as the action hardly diminished over 12 rounds.
Arthur barely secured the verdict with judges scorecards of 114-114, 115-113 and clearer margin, but each competitor were persistent and full of heart, everything their idol the legend represented.
