British light-heavyweight Buatsi earned a win yet underwhelming start to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But Parker had his moments, landing some telling individual punches in a contest where the styles failed to mesh, with constant grabbing disrupting the fight.
The officials judged it 96-94 for to the winner, with the third a even score.
"It wasn't my greatest display but what do champions do? They prevail," Buatsi stated in the ringside as he was met by negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to claim a 20th pro success.
Some ringside observers believed the challenger, 31, should have been awarded the decision but the British boxer suffered the second defeat of his 28-fight career.
Buatsi Claims Triumph in Slow Match
The fighter's advancement has stalled in the past few years through management issues and extended periods of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to realize his potential - maybe in what seems like a final roll of the dice - under fresh management.
He began cautiously, with both competitors prepared to overcommit in a tentative early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was participating in his second fight at the higher weight class.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who operated with a solid defense to barely take the cleaner periods.
The crowd's patience diminished because of constant clinching, with Parker falling to the floor multiple occasions during clinches.
Parker ended stronger, but many rounds were hard to judge. However, ex-champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Tribute Fuels All-Manchester Contest
In the secondary fight, Arthur beat Bradley Rea by divided decision in a outstanding Manchester vs Manchester fight to win the European light-heavyweight championship.
The venue fell silent for a profoundly moving memorial before the fight as a bell ceremony tolled in honor of Manchester's own Ricky Hatton, who died aged 46 in recently.
It was the first major televised match card in the location since Hatton's death. As the last bell disappeared, the quiet became a roar of "there's only one Ricky Hatton".
The fighting within the ring reflected the emotion. Arthur was knocked down by a significant blow directly to the jaw in the second round, standing uncertainly to his position on the count of eight.
But the traditional red equipment of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was damaged early, significant bruising appearing under his eye as the fighters exchanged powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the pace hardly diminished over 12 rounds.
The victor edged the verdict with scoring tallies of 114-114, close margin and clearer margin, but the two athletes were relentless and full of heart, everything their inspiration the legend stood for.
