British light heavyweight Buatsi made a winning yet underwhelming beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a competitive ten-round contest at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful individual punches in a fight where the styles didn't complement each other, with frequent clinching disrupting the contest.
The officials had it 96-94 to the winner, with the third a even score.
"It wasn't my best performance but what do champions do? They win," the victor commented in the ringside as he was greeted with negative reactions from the spectators.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers thought the challenger, thirty-one, deserved the victory but the British boxer suffered the second loss of his 28-bout professional journey.
The Champion Secures Win in Uneventful Affair
Buatsi's progress has plateaued in recent years through contract problems and extended periods of inactivity.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to realize his potential - perhaps in what seems like a last chance - under recent support.
He opened tentatively, with both competitors prepared to overcommit in a tentative early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand in the contest, was making just his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, creating difficulties for the favorite, who utilized a tight guard to narrowly win the better periods.
The audience's tolerance diminished during regular grabbing, with Parker slipping to the canvas various instances during grappling.
Parker finished the stronger, but multiple periods were challenging to assess. Although, ex-champion the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, giving Buatsi just one round.
Buatsi moves on, but with the caliber of heavy hitter Benavidez, and Russian star Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Memorial Fuels Manchester Derby Battle
In the secondary fight, Lyndon Arthur overcame Rea by close verdict in a terrific all-Manchester battle to win the European light-heavyweight title.
The arena became quiet for a extremely emotional memorial before the fight as ten bells sounded in remembrance of local hero Hatton, who passed away at age 46 in last month.
It was the premier televised boxing event in the location since Hatton's death. As the last bell faded, the quiet became a chant of "there's only one Hatton".
The fighting inside the ropes matched the feeling. The eventual winner was sent to the canvas by a left hook flush on the chin in the early round, getting up unsteadily to his footing on the eight count.
But the traditional red attire of Arthur soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was injured quickly, significant bruising appearing under his orbital area as the pair landed punishing blows.
Rea, 27, landed power punches but Arthur, 34, fought fire with fire with powerful upward punches as the intensity hardly diminished over 12 rounds.
Arthur narrowly won the decision with official scores of draw, close margin and 115-112, but the two athletes were persistent and brave, everything their inspiration the legend embodied.
