UK light-heavyweight Buatsi earned a win yet disappointing debut to life under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a tight 10-round contest at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful individual punches in a match where the techniques failed to mesh, with frequent clinching marring the contest.
The officials had it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my best display but what defines champions? They succeed," the victor commented in the ring as he was greeted with boos from the audience.
The British fighter returned to winning ways after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a 20th pro success.
Various analysts felt Parker, thirty-one, should have been awarded the win but the British boxer experienced the second loss of his 28-fight career.
Buatsi Secures Triumph in Uneventful Match
Buatsi's progress has stalled in the past few years through contract problems and long spells of lack of fights.
Earlier forecast as the future of British boxing, he now stands trying to realize his potential - maybe in what seems like a last chance - under recent support.
He began cautiously, with neither fighter ready to be aggressive in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who operated with a tight guard to edge the better periods.
The spectators' acceptance wore thin during constant clinching, with Parker falling to the floor multiple occasions during grappling.
The underdog finished the stronger, but several stanzas were challenging to assess. Although, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the presence of power puncher Benavidez, and Russian champion Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Hatton Memorial Fuels Manchester Derby Contest
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a outstanding local rivalry fight to secure the continental belt.
The stadium fell silent for a extremely emotional tribute ahead of the contest as a bell ceremony tolled in honor of local hero Hatton, who passed away aged 46 in recently.
It was the premier televised boxing event in the city since Hatton's death. As the last bell faded, the silence became a roar of "only one Ricky Hatton".
The competition during the bout equaled the sentiment. The eventual winner was knocked down by a powerful punch flush on the face in the initial stage, rising shakily to his position on the referee's count.
But the red-colored equipment of Arthur soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was marked up early, significant bruising forming under his orbital area as the pair traded powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the intensity seldom decreased over 12 rounds.
Arthur narrowly won the result with scoring tallies of draw, narrow lead and clearer margin, but both fighters were relentless and courageous, everything their hero the legend embodied.
