British light-heavyweight Buatsi made a winning yet unimpressive start to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a split decision in a competitive 10-round contest at the boxing arena.
But the challenger landed significant shots, connecting with powerful clean blows in a contest where the techniques failed to mesh, with excessive holding spoiling the fight.
The scoring judges judged it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They win," the victor said in the ring as he was met by negative reactions from the crowd.
The British fighter got back to winning after his maiden career setback - an memorable fight with his previous opponent in last winter - to secure a 20th pro success.
Various analysts felt Parker, thirty-one, deserved the win but the Derbyshire fighter experienced the second loss of his 28-match professional journey.
The Champion Claims Triumph in Slow Affair
Buatsi's progress has slowed in the past few years through promotional disputes and considerable time of lack of fights.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to realize his potential - possibly in what appears to be a final roll of the dice - under recent support.
He started carefully, with both competitors willing to be aggressive in a cagey opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was participating in his second fight at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for Buatsi, who worked behind a protective stance to narrowly win the better periods.
The audience's tolerance diminished during frequent holding, with Parker falling to the floor several times during grappling.
The underdog closed well, but many rounds were difficult to score. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
The victor progresses, but with the likes of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - judging by this showing - still seems difficult.
Hatton Tribute Inspires Manchester Derby Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a terrific all-Manchester fight to secure the continental belt.
The stadium fell silent for a extremely emotional tribute before the fight as ten bells rang in memory of local hero Hatton, who succumbed at age 46 in September.
It was the first major televised boxing event in the urban center since Hatton's death. As the last bell ended, the silence transitioned to a chant of "there's only one Hatton".
The competition inside the ropes matched the sentiment. Arthur was floored by a significant blow flush on the face in the early round, rising shakily to his feet on the referee's count.
But the traditional red equipment of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was injured soon, noticeable damage appearing under his orbital area as the duo traded punishing blows.
Rea, 27, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace rarely dropped over 12 rounds.
Arthur barely secured the decision with scoring tallies of 114-114, 115-113 and clearer margin, but both fighters were persistent and courageous, all the qualities their inspiration the legend embodied.
