UK light-heavyweight Buatsi earned a win yet underwhelming debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a close ten-round fight at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful single shots in a contest where the techniques didn't complement each other, with frequent clinching marring the fight.
The scoring judges judged it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best showing but how do champions respond? They prevail," Buatsi commented in the arena as he was met by negative reactions from the audience.
The British fighter bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, merited the win but the contender experienced the second setback of his 28-bout professional journey.
The Champion Claims Victory in Slow Encounter
The fighter's advancement has plateaued in recent years through contract problems and extended periods of inactivity.
Once tipped as the next star of UK boxing, he now is positioned trying to achieve expectations - possibly in what seems like a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors willing to take risks in a tentative initial rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was making just his second appearance at light-heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for the favorite, who utilized a solid defense to barely take the cleaner periods.
The audience's tolerance diminished because of constant clinching, with Parker going down multiple occasions during clinches.
Parker finished the stronger, but many rounds were hard to judge. Although, ex-champion the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, giving Buatsi just a single round.
The victor moves on, but with the likes of hard hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Homage Inspires Manchester Derby Battle
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a excellent local rivalry battle to secure the European light-heavyweight title.
The venue fell silent for a profoundly moving homage prior to the bout as a bell ceremony tolled in memory of local hero Ricky Hatton, who succumbed 46 years old in recently.
It was the premier televised match card in the urban center since Hatton's passing. As the last bell faded, the quiet became a chant of "there's only one Ricky Hatton".
The action inside the ropes reflected the feeling. The eventual winner was knocked down by a left hook squarely on the chin in the initial stage, standing uncertainly to his footing on the referee's count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was marked up early, heavy swelling appearing under his eye as the duo landed punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over 12 rounds.
The victor edged the verdict with scoring tallies of even score, 115-113 and wider gap, but both fighters were persistent and full of heart, all the qualities their idol Hatton represented.
