UK light heavyweight Buatsi earned a win yet underwhelming debut to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a close ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful clean blows in a contest where the techniques failed to mesh, with frequent clinching disrupting the action.
The scoring judges had it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what do champions do? They prevail," Buatsi commented in the arena as he was met by boos from the spectators.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts believed the challenger, 31, merited the win but the Derbyshire fighter experienced the second loss of his 28-bout professional journey.
Buatsi Secures Triumph in Uneventful Match
His career development has stalled in recent times through contract problems and considerable time of inactivity.
Previously predicted as the rising talent of British boxing, he now stands trying to realize his potential - perhaps in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter willing to take risks in a cagey opening few rounds.
Parker, 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 making just his second fight at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who operated with a solid defense to barely take the cleaner rounds.
The crowd's patience diminished during regular grabbing, with Parker slipping to the canvas several times during close exchanges.
The underdog ended stronger, but several stanzas were challenging to assess. However, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, awarding Buatsi just one round.
Buatsi moves on, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Memorial Fuels All-Manchester Contest
In the supporting bout, Lyndon Arthur defeated Bradley Rea by divided decision in a excellent local rivalry fight to secure the continental belt.
The venue fell silent for a extremely emotional tribute before the fight as a bell ceremony rang in honor of the city's native Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the final chime faded, the stillness became a roar of "only one Ricky Hatton".
The fighting during the bout matched the sentiment. Arthur was knocked down by a powerful punch flush on the face in the second round, rising shakily to his feet on the eight count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was damaged quickly, noticeable damage appearing under his orbital area as the fighters landed punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with powerful upward punches as the action seldom decreased over 12 rounds.
Arthur barely secured the decision with scoring tallies of 114-114, close margin and wider gap, but each competitor were determined and full of heart, everything their hero the legend stood for.
