British light-heavyweight Buatsi earned a win yet unimpressive debut to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a majority decision in a close 10-round bout at the boxing arena.
But Parker landed significant shots, landing some telling single shots in a fight where the approaches didn't complement each other, with frequent clinching marring the action.
Two judges had it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my greatest performance but what do champions do? They prevail," Buatsi stated in the ring as he was met by disapproval from the spectators.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Various analysts felt the challenger, thirty-one, deserved the decision but the British boxer endured the second defeat of his 28-bout career.
The Champion Earns Victory in Uneventful Encounter
Buatsi's progress has slowed in the past few years through contract problems and considerable time of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under recent support.
He began cautiously, with both competitors prepared to overcommit in a cagey initial rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was competing in only his second bout at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a solid defense to narrowly win the more effective periods.
The spectators' acceptance diminished amid constant clinching, with the challenger slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but several stanzas were difficult to score. Although, former world champion the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, giving Buatsi just one round.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still seems difficult.
Hatton Memorial Fuels Manchester Derby Fight
In the co-main event, Lyndon Arthur defeated Bradley Rea by close verdict in a terrific all-Manchester contest to capture the European light heavyweight belt.
The stadium fell silent for a profoundly moving memorial prior to the bout as ten bells tolled in memory of Manchester's own Hatton, who passed away at age 46 in September.
It was the premier televised match card in the location since the passing of Hatton. As the last bell faded, the quiet became a chant of "there's just one Hatton".
The competition inside the ropes equaled the feeling. The eventual winner was knocked down by a left hook flush on the face in the early round, getting up unsteadily to his footing on the eight count.
But the traditional red attire of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was injured quickly, significant bruising developing under his eye as the fighters traded punishing blows.
Rea, 27, delivered effective strikes but the champion, thirty-four, responded in kind with effective uppercuts as the pace rarely dropped over the full distance.
Arthur barely secured the decision with official scores of draw, 115-113 and clearer margin, but both fighters were persistent and full of heart, exactly what their inspiration the legend embodied.
