UK light heavyweight Buatsi made a winning yet disappointing start to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a tight ten-round fight at the Manchester venue.
But Parker landed significant shots, landing some telling individual punches in a contest where the techniques didn't complement each other, with frequent clinching spoiling the fight.
The officials scored it 96-94 to the winner, with the third a even score.
"It wasn't my finest display but what do champions do? They win," Buatsi commented in the ringside as he was greeted with boos from the audience.
The Londoner bounced back after his initial pro loss - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Several boxing experts thought the challenger, thirty-one, merited the decision but the Derbyshire fighter endured the second defeat of his 28-match career.
The Champion Claims Win in Uneventful Encounter
His career development has plateaued in the past few years through promotional disputes and long spells of lack of fights.
Once tipped as the rising talent of UK boxing, he now finds himself trying to achieve expectations - maybe in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors willing to be aggressive in a tentative 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 in the contest, was competing in only his second bout at light heavyweight.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who operated with a solid defense to narrowly win the better rounds.
The spectators' acceptance wore thin because of frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
Parker closed well, but many rounds were difficult to score. Nevertheless, previous titleholder the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi advances, but with the presence of hard hitter David Benavidez, and Russian star Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Memorial Inspires All-Manchester Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a terrific all-Manchester fight to win the continental championship.
The venue grew hushed for a deeply poignant tribute ahead of the contest as a bell ceremony sounded in memory of Manchester's own Hatton, who succumbed aged 46 in last month.
It was the first major televised fight night in the urban center since Hatton's death. As the final chime faded, the quiet transitioned to a chant of "there's just one Ricky Hatton".
The action within the ring equaled the feeling. The eventual winner was floored by a significant blow squarely on the jaw in the early round, standing uncertainly to his position on the eight count.
But the Manchester United-red equipment of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was damaged soon, noticeable damage forming under his eye as the duo exchanged hard punches.
Rea, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the pace seldom decreased over 12 rounds.
Arthur narrowly won the decision with scoring tallies of even score, close margin and wider gap, but both fighters were persistent and courageous, everything their inspiration the legend stood for.
