British light heavyweight Buatsi secured a victory yet disappointing beginning to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a split decision in a close 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful single shots in a match where the styles failed to mesh, with excessive holding spoiling the action.
The officials judged it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best display but what do champions do? They prevail," Buatsi commented in the ring as he was met by boos from the crowd.
The Londoner got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a 20th career victory.
Several boxing experts thought Parker, 31, should have been awarded the win but the contender experienced the second setback of his 28-fight career.
The Champion Claims Win in Dull Match
His career development has plateaued in the past few years through promotional disputes and considerable time of inactivity.
Previously predicted as the future of British boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under recent support.
He started carefully, with the two boxers ready to be aggressive in a tentative opening few rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second bout at light heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who utilized a protective stance to barely take the better rounds.
The crowd's patience decreased during regular grabbing, with the challenger slipping to the canvas several times during close exchanges.
The underdog finished the stronger, but several stanzas were difficult to score. Nevertheless, ex-champion the boxing analyst - working with the broadcast network - had it particularly wide for Parker, giving Buatsi just only one stanza.
Buatsi progresses, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Homage Fuels Local Rivalry Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific all-Manchester fight to capture the European light heavyweight title.
The venue became quiet for a profoundly moving memorial ahead of the contest as ten bells tolled in memory of Manchester's own Hatton, who died aged 46 in September.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the last bell disappeared, the silence became a shout of "only one Ricky Hatton".
The competition inside the ropes equaled the sentiment. Arthur was floored by a significant blow flush on the jaw in the initial stage, getting up unsteadily to his footing on the count of eight.
But the Manchester United-red shorts of Arthur soon came forward again. Across the ring, Rea - in opposing blue - was marked up early, significant bruising appearing under his eye as the duo landed powerful shots.
The challenger, 27, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the intensity hardly diminished over the full distance.
The victor narrowly won the verdict with scoring tallies of draw, narrow lead and wider gap, but each competitor were relentless and courageous, all the qualities their inspiration the legend represented.
