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 work rate seemingly secured him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a match where the techniques didn't complement each other, with frequent clinching marring the contest.
Two judges had it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my finest showing but what defines champions? They succeed," the victor said in the ringside as he was met by negative reactions from the spectators.
The Londoner got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts thought the challenger, 31, deserved the victory but the Derbyshire fighter experienced the second defeat of his 28-fight career.
The fighter's advancement has stalled in recent times through contract problems and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now is positioned trying to realize his potential - perhaps in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with both competitors willing to be aggressive in a calculated opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after damaging his hand mid-fight, was participating in his second fight at light heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for the favorite, who utilized a solid defense to narrowly win the cleaner stanzas.
The audience's tolerance wore thin because of regular grabbing, with the challenger falling to the floor multiple occasions during grappling.
The underdog closed well, but several stanzas were hard to judge. Although, previous titleholder the boxing analyst - working with Dazn - had it strongly leaning for the challenger, scoring for Buatsi just one round.
The victor advances, but with the presence of power puncher David Benavidez, and Russian star Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
In the co-main event, Lyndon Arthur overcame Bradley Rea by divided decision in a excellent all-Manchester battle to capture the European light-heavyweight championship.
The stadium fell silent for a deeply poignant homage prior to the bout as a bell ceremony tolled in memory of Manchester's own Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the final chime faded, the stillness gave way to a shout of "only one Ricky Hatton".
The fighting within the ring equaled the feeling. Arthur was floored by a left hook directly to the jaw in the early round, standing uncertainly to his position on the referee's count.
But the traditional red shorts of Arthur soon pressed ahead again. On the opposite side, Rea - in opposing blue - was damaged soon, noticeable damage forming under his face as the fighters landed punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with powerful upward punches as the action hardly diminished over the full distance.
Arthur barely secured the verdict with scoring tallies of draw, narrow lead and 115-112, but each competitor were persistent and brave, everything their idol the legend stood for.
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