UK light-heavyweight Buatsi secured a victory yet disappointing debut to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a close 10-round bout at the Co-op Live Arena.
But the challenger found success, landing some telling clean blows in a contest where the approaches failed to mesh, with excessive holding marring the action.
The scoring judges judged it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my best performance but what defines champions? They win," Buatsi said in the ringside as he was greeted with boos from the audience.
The Londoner returned to winning ways after his initial pro loss - an epic battle with his previous opponent in February - to claim a 20th pro success.
Various analysts thought Parker, 31, merited the decision but the contender endured the second defeat of his 28-fight career.
The Champion Secures Triumph in Uneventful Match
Buatsi's progress has plateaued in recent times through contract problems and considerable time of inactivity.
Once tipped as the future of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under recent support.
He began cautiously, with the two boxers 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 fight at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a solid defense to narrowly win the more effective stanzas.
The crowd's patience diminished during regular grabbing, with Parker going down several times during close exchanges.
Parker ended stronger, but multiple periods were hard to judge. Although, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi advances, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Inspires All-Manchester Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific local rivalry fight to secure the European light heavyweight belt.
The arena fell silent for a deeply poignant memorial before the fight as a bell ceremony tolled in remembrance of the city's native Hatton, who passed away 46 years old in recently.
It was the first major televised match card in the urban center since the passing of Hatton. As the last bell ended, the stillness became a shout of "there's just one Ricky Hatton".
The action during the bout matched the emotion. Arthur was floored by a significant blow squarely on the jaw in the initial stage, standing uncertainly to his footing on the referee's count.
But the traditional red equipment of Arthur soon pressed ahead again. Across the ring, Rea - in competitive blue - was injured quickly, significant bruising developing under his face as the fighters exchanged punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, 34, responded in kind with powerful upward punches as the intensity seldom decreased over the full distance.
Arthur barely secured the result with scoring tallies of even score, 115-113 and 115-112, but both fighters were persistent and courageous, everything their hero Hatton stood for.
