UK light heavyweight Buatsi secured a victory yet unimpressive beginning to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a split decision in a competitive 10-round bout at the Co-op Live Arena.
But Parker landed significant shots, landing some telling individual punches in a contest where the styles never quite clicked, with constant grabbing disrupting the contest.
The scoring judges had it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my finest showing but what do champions do? They win," Buatsi said in the ring as he was greeted with negative reactions from the spectators.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to secure a 20th pro success.
Various analysts believed the challenger, thirty-one, should have been awarded the victory but the British boxer suffered the second loss of his 28-bout career.
Buatsi Secures Triumph in Slow Match
His career development has slowed in the past few years through contract problems and long spells of inactivity.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under recent support.
He opened tentatively, with the two boxers prepared to overcommit in a calculated early stages.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was making just his second fight at light-heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for Buatsi, who utilized a solid defense to narrowly win the cleaner periods.
The spectators' acceptance wore thin because of regular grabbing, with Parker slipping to the canvas various instances during grappling.
Parker finished the stronger, but many rounds were difficult to score. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi moves on, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Homage Motivates Local Rivalry Battle
In the secondary fight, Lyndon Arthur defeated Bradley Rea by close verdict in a outstanding all-Manchester contest to win the European light-heavyweight title.
The arena became quiet for a profoundly moving tribute ahead of the contest as ten bells sounded in remembrance of the city's native Hatton, who passed away 46 years old in September.
It was the first major televised match card in the location since the passing of Hatton. As the last bell disappeared, the silence gave way to a shout of "there's only one Ricky Hatton".
The competition within the ring matched the emotion. The eventual winner was knocked down by a powerful punch flush on the jaw in the early round, rising shakily to his position on the referee's count.
But the red-colored shorts of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was marked up soon, noticeable damage developing under his face as the fighters traded powerful shots.
The challenger, 27, connected with strong blows but Arthur, thirty-four, matched the intensity with powerful upward punches as the intensity seldom decreased over twelve rounds.
The victor barely secured the decision with judges scorecards of draw, 115-113 and 115-112, but each competitor were determined and courageous, everything their hero Hatton stood for.
