British light-heavyweight Buatsi earned a win yet disappointing debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But Parker had his moments, delivering effective individual punches in a match where the approaches didn't complement each other, with constant grabbing marring the action.
Two judges had it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my greatest performance but what do champions do? They win," the victor said in the ring as he was met by negative reactions from the spectators.
The British fighter bounced back after his initial pro loss - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Various analysts felt the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter experienced the second loss of his 28-fight career.
Buatsi Claims Win in Uneventful Encounter
His career development has stalled in the past few years through contract problems and considerable time of lack of fights.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under fresh management.
He started carefully, with the two boxers prepared to be aggressive in a calculated early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in 2022 after breaking his hand mid-fight, was participating in his second bout at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who utilized a tight guard to edge the more effective rounds.
The spectators' acceptance diminished because of regular grabbing, with the challenger going down several times during close exchanges.
The underdog ended stronger, but many rounds were challenging to assess. Nevertheless, previous titleholder the boxing analyst - working with Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor advances, but with the caliber of hard hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Homage Fuels All-Manchester Contest
In the secondary fight, Lyndon Arthur beat Bradley Rea by close verdict in a excellent all-Manchester fight to capture the European light heavyweight belt.
The venue fell silent for a extremely emotional homage prior to the bout as a bell ceremony tolled in remembrance of the city's native Hatton, who succumbed aged 46 in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the final chime disappeared, the silence transitioned to a shout of "there's just one Ricky Hatton".
The fighting within the ring matched the sentiment. The eventual winner was floored by a left hook squarely on the jaw in the second round, standing uncertainly to his feet on the eight count.
But the Manchester United-red equipment of the fighter soon came forward again. From the other corner, Rea - in opposing blue - was injured soon, heavy swelling appearing under his eye as the duo landed punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with powerful upward punches as the pace seldom decreased over 12 rounds.
Arthur barely secured the verdict with scoring tallies of draw, narrow lead and 115-112, but the two athletes were persistent and full of heart, all the qualities their hero Hatton represented.
