UK light-heavyweight Buatsi made a winning yet underwhelming beginning to his career under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a tight ten-round contest at the Manchester venue.
But the challenger found success, connecting with powerful individual punches in a contest where the styles didn't complement each other, with constant grabbing spoiling the action.
The officials scored it 96-94 for to the winner, with the third a 95-95.
"It wasn't my greatest performance but how do champions respond? They succeed," Buatsi stated in the arena as he was greeted with boos from the crowd.
The Londoner got back to winning after his first professional defeat - an memorable fight with Callum Smith in February - to claim a 20th career victory.
Some ringside observers felt the challenger, 31, should have been awarded the victory but the contender endured the second defeat of his 28-bout career.
Buatsi Earns Win in Dull Affair
Buatsi's progress has slowed in the past few years through management issues and long spells of lack of fights.
Previously predicted as the next star of British boxing, he now stands trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with neither fighter willing to overcommit in a calculated opening few rounds.
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 light-heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for Buatsi, who operated with a protective stance to barely take the cleaner stanzas.
The spectators' acceptance decreased because of constant clinching, with Parker slipping to the canvas various instances during grappling.
Parker closed well, but many rounds were challenging to assess. However, ex-champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor progresses, but with the presence of hard hitter David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Memorial Inspires All-Manchester Contest
In the secondary fight, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent local rivalry battle to win the European light-heavyweight belt.
The stadium fell silent for a profoundly moving memorial ahead of the contest as ten bells sounded in honor of the city's native Ricky Hatton, who passed away aged 46 in recently.
It was the premier televised fight night in the city since Hatton's death. As the concluding sound ended, the quiet gave way to a roar of "there's only one Ricky Hatton".
The fighting inside the ropes matched the sentiment. Arthur was floored by a powerful punch flush on the face in the early round, standing uncertainly to his footing on the eight count.
But the Manchester United-red attire of the fighter soon pressed ahead again. From the other corner, Rea - in rival City blue - was injured quickly, noticeable damage forming under his orbital area as the duo landed punishing blows.
Rea, twenty-seven, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the pace rarely dropped over 12 rounds.
Arthur edged the result with scoring tallies of even score, 115-113 and wider gap, but both fighters were relentless and full of heart, exactly what their idol the legend stood for.
