British light-heavyweight Buatsi secured a victory yet unimpressive beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a competitive ten-round fight at the boxing arena.
But the challenger found success, landing some telling individual punches in a fight where the styles failed to mesh, with excessive holding spoiling the fight.
The scoring judges scored it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my finest performance but what defines champions? They win," the victor stated in the ringside as he was greeted with boos from the audience.
The British fighter got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to earn a 20th pro success.
Various analysts believed the challenger, thirty-one, deserved the victory but the Derbyshire fighter experienced the second defeat of his 28-bout career.
The Champion Claims Triumph in Slow Match
His career development has slowed in recent years through management issues and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now stands trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with both competitors ready to be aggressive in a tentative opening few rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was participating in his second bout at light-heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for Buatsi, who operated with a solid defense to edge the cleaner stanzas.
The spectators' acceptance diminished because of frequent holding, with Parker falling to the floor several times during grappling.
The underdog ended stronger, but multiple periods were difficult to score. Although, previous titleholder the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
The victor advances, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Tribute Inspires All-Manchester Battle
In the supporting bout, Lyndon Arthur defeated Bradley Rea by split-decision in a terrific local rivalry fight to win the European light-heavyweight title.
The stadium fell silent for a extremely emotional homage ahead of the contest as ten bells tolled in honor of the city's native Ricky Hatton, who succumbed at age 46 in recently.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the concluding sound disappeared, the stillness transitioned to a roar of "there's just one Ricky Hatton".
The fighting inside the ropes reflected the sentiment. Arthur was knocked down by a left hook squarely on the face in the second round, standing uncertainly to his position on the eight count.
But the traditional red shorts of Arthur soon advanced again. On the opposite side, the opponent - in rival City blue - was marked up soon, significant bruising forming under his orbital area as the fighters landed punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, responded in kind with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor narrowly won the result with official scores of 114-114, narrow lead and 115-112, but the two athletes were relentless and courageous, exactly what their inspiration the legend embodied.
