British light-heavyweight Buatsi earned a win yet underwhelming beginning to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a tight 10-round contest at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful clean blows in a contest where the approaches failed to mesh, with excessive holding spoiling the fight.
The officials scored it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest performance but how do champions respond? They prevail," the victor stated in the ring as he was greeted with negative reactions from the crowd.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers thought the challenger, 31, should have been awarded the victory but the Derbyshire fighter suffered the second defeat of his 28-fight professional journey.
Buatsi Claims Triumph in Slow Affair
His career development has plateaued in the past few years through promotional disputes and extended periods of inactivity.
Earlier forecast as the future of the British fight scene, he now is positioned trying to realize his potential - possibly in what seems like a ultimate opportunity - under recent support.
He started carefully, with the two boxers prepared to be aggressive in a tentative initial rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second bout at light heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for Buatsi, who utilized a solid defense to narrowly win the more effective periods.
The spectators' acceptance wore thin during frequent holding, with Parker slipping to the canvas several times during clinches.
The underdog finished the stronger, but several stanzas were difficult to score. Although, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Tribute Fuels All-Manchester Battle
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent all-Manchester contest to win the European light heavyweight title.
The arena became quiet for a extremely emotional homage prior to the bout as ten bells tolled in honor of the city's native Hatton, who passed away at age 46 in September.
It was the initial significant broadcast fight night in the city since Hatton's death. As the final chime disappeared, the silence gave way to a roar of "there's just one Ricky Hatton".
The action inside the ropes equaled the feeling. Arthur was floored by a powerful punch directly to the face in the initial stage, getting up unsteadily to his footing on the referee's count.
But the traditional red equipment of the fighter soon advanced again. From the other corner, Rea - in opposing blue - was injured early, significant bruising appearing under his orbital area as the pair landed hard punches.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace rarely dropped over twelve rounds.
The victor edged the decision with judges scorecards of draw, 115-113 and wider gap, but the two athletes were persistent and brave, exactly what their hero Hatton embodied.
