British light heavyweight Buatsi secured a victory yet unimpressive beginning to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a tight 10-round contest at the Manchester venue.
But Parker found success, delivering effective single shots in a contest where the approaches never quite clicked, with frequent clinching spoiling the action.
The scoring judges judged it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my greatest performance but how do champions respond? They prevail," Buatsi stated in the ringside as he was greeted with negative reactions from the audience.
The Londoner bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts believed Parker, thirty-one, should have been awarded the decision but the contender endured the second setback of his 28-fight career.
Buatsi Secures Victory in Dull Encounter
Buatsi's progress has stalled in recent years through contract problems and long spells of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with both competitors willing to be aggressive in a tentative initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was making just his second appearance at light heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who worked behind a solid defense to edge the more effective periods.
The audience's tolerance diminished during frequent holding, with the challenger slipping to the canvas several times during clinches.
The underdog finished the stronger, but multiple periods were difficult to score. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
The victor advances, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Tribute Inspires Manchester Derby Fight
In the supporting bout, Lyndon Arthur beat Rea by close verdict in a excellent local rivalry battle to capture the European light heavyweight belt.
The arena became quiet for a deeply poignant memorial prior to the bout as ten bells rang in remembrance of the city's native Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the last bell disappeared, the quiet transitioned to a roar of "only one Hatton".
The competition during the bout reflected the sentiment. The eventual winner was sent to the canvas by a significant blow flush on the face in the initial stage, rising shakily to his footing on the eight count.
But the red-colored equipment of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was injured quickly, significant bruising appearing under his orbital area as the fighters traded punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with effective uppercuts as the pace rarely dropped over 12 rounds.
Arthur barely secured the verdict with official scores of even score, close margin and wider gap, but the two athletes were persistent and brave, exactly what their idol Hatton embodied.
