British light heavyweight Buatsi secured a victory yet disappointing beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a split decision in a close ten-round bout at the boxing arena.
But Parker landed significant shots, delivering effective clean blows in a match where the techniques never quite clicked, with excessive holding spoiling the action.
The scoring judges had it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my best showing but what do champions do? They prevail," the victor commented in the arena as he was greeted with negative reactions from the audience.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts believed Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter experienced the second setback of his 28-match career.
Buatsi Claims Win in Dull Match
Buatsi's progress has plateaued in recent years through management issues and considerable time of lack of fights.
Earlier forecast as the future of the British fight scene, he now stands trying to achieve expectations - possibly in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter prepared to overcommit in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second appearance at the higher weight class.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who operated with a solid defense to edge the better periods.
The spectators' acceptance wore thin amid regular grabbing, with Parker falling to the floor several times during clinches.
The underdog closed well, but multiple periods were challenging to assess. Nevertheless, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, giving Buatsi just one round.
The victor progresses, but with the presence of power puncher David Benavidez, and Russian star Bivol leading the category, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Tribute Inspires Local Rivalry Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a terrific all-Manchester fight to capture the European light heavyweight belt.
The arena fell silent for a deeply poignant homage prior to the bout as a bell ceremony rang in remembrance of local hero Hatton, who passed away 46 years old in September.
It was the first major televised boxing event in the urban center since Hatton's death. As the final chime ended, the quiet became a chant of "there's only one Ricky Hatton".
The competition during the bout reflected the feeling. Arthur was floored by a left hook flush on the face in the second round, getting up unsteadily to his feet on the count of eight.
But the red-colored shorts of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was marked up soon, significant bruising appearing under his eye as the pair exchanged punishing blows.
The challenger, 27, connected with strong blows but Arthur, 34, responded in kind with powerful upward punches as the action rarely dropped over the full distance.
The victor narrowly won the decision with official scores of draw, narrow lead and wider gap, but the two athletes were relentless and full of heart, all the qualities their idol Hatton embodied.
