UK light heavyweight Buatsi made a winning yet disappointing debut to life under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a majority decision in a competitive 10-round fight at the Manchester venue.
But Parker landed significant shots, landing some telling single shots in a match where the styles didn't complement each other, with frequent clinching spoiling the action.
The scoring judges had it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They win," the victor stated in the arena as he was faced disapproval from the audience.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in February - to claim a twentieth professional win.
Various analysts believed Parker, thirty-one, should have been awarded the win but the Derbyshire fighter endured the second setback of his 28-match professional journey.
Buatsi Earns Win in Slow Affair
Buatsi's progress has plateaued in recent times through management issues and long spells of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with both competitors willing to take risks in a tentative initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for the favorite, who worked behind a protective stance to narrowly win the cleaner periods.
The crowd's patience wore thin amid regular grabbing, with the challenger slipping to the canvas multiple occasions during grappling.
The underdog closed well, but many rounds were difficult to score. However, former world champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor moves on, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Fuels Manchester Derby Fight
In the supporting bout, Lyndon Arthur overcame Rea by close verdict in a outstanding Manchester vs Manchester battle to capture the European light heavyweight belt.
The venue fell silent for a extremely emotional memorial prior to the bout as ten bells sounded in honor of the city's native Hatton, who passed away aged 46 in last month.
It was the premier televised boxing event in the location since Hatton's passing. As the final chime ended, the stillness became a roar of "there's only one Ricky Hatton".
The fighting inside the ropes equaled the feeling. Arthur was sent to the canvas by a powerful punch directly to the jaw in the initial stage, standing uncertainly to his position on the count of eight.
But the red-colored attire of the fighter soon came forward again. Across the ring, the opponent - in rival City blue - was marked up soon, heavy swelling forming under his face as the pair landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action hardly diminished over 12 rounds.
Arthur narrowly won the decision with judges scorecards of 114-114, narrow lead and 115-112, but both fighters were persistent and courageous, everything their idol the legend embodied.
