UK light-heavyweight Buatsi made a winning yet unimpressive debut to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a split decision in a competitive 10-round bout at the Co-op Live Arena.
But Parker found success, delivering effective clean blows in a contest where the approaches failed to mesh, with frequent clinching spoiling the action.
Two judges had it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my greatest display but how do champions respond? They prevail," the victor said in the arena 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 last winter - to secure a twentieth professional win.
Various analysts believed the challenger, thirty-one, merited the decision but the Derbyshire fighter endured the second loss of his 28-match career.
Buatsi Secures Victory in Uneventful Encounter
The fighter's advancement has slowed in recent years through management issues and considerable time of inactivity.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - maybe in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with both competitors ready to take risks in a calculated early stages.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after damaging his hand mid-fight, was making just his second fight at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for the favorite, who worked behind a solid defense to edge the better periods.
The audience's tolerance diminished during regular grabbing, with Parker falling to the floor several times during grappling.
Parker ended stronger, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
Buatsi progresses, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Homage Motivates All-Manchester Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding local rivalry fight to secure the European light-heavyweight belt.
The stadium became quiet for a deeply poignant homage prior to the bout as 10 bells rang in remembrance of the city's native Hatton, who succumbed at age 46 in last month.
It was the premier televised boxing event in the city since the passing of Hatton. As the last bell ended, the stillness became a shout of "only one Ricky Hatton".
The competition inside the ropes equaled the sentiment. Arthur was sent to the canvas by a powerful punch directly to the face in the initial stage, rising shakily to his feet on the referee's count.
But the red-colored attire of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was injured soon, noticeable damage developing under his orbital area as the fighters landed powerful shots.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with powerful upward punches as the action rarely dropped over the full distance.
Arthur narrowly won the verdict with official scores of 114-114, close margin and clearer margin, but both fighters were relentless and courageous, everything their inspiration Hatton embodied.
