British light heavyweight Buatsi secured a victory yet unimpressive debut to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a split decision in a tight ten-round contest at the Manchester venue.
But Parker had his moments, connecting with powerful single shots in a fight where the approaches didn't complement each other, with constant grabbing spoiling the fight.
The scoring judges judged it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my greatest display but what do champions do? They win," the victor said in the arena as he was met by negative reactions from the crowd.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers believed Parker, thirty-one, merited the decision but the contender experienced the second defeat of his 28-match career.
Buatsi Claims Triumph in Dull Match
His career development has stalled in the past few years through contract problems and long spells of inactivity.
Once tipped as the future 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 opened tentatively, with both competitors ready to overcommit in a calculated opening few rounds.
Parker, whose sole prior loss came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was participating in his second bout at light heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for Buatsi, who worked behind a solid defense to edge the better periods.
The crowd's patience decreased because of regular grabbing, with Parker going down various instances during grappling.
Parker ended stronger, but many rounds were challenging to assess. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, giving Buatsi just only one stanza.
The victor moves on, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Hatton Memorial Motivates All-Manchester Contest
In the co-main event, Lyndon Arthur defeated Rea by close verdict in a excellent local rivalry battle to capture the European light heavyweight belt.
The stadium became quiet for a profoundly moving tribute ahead of the contest as a bell ceremony rang in remembrance of the city's native Hatton, who succumbed 46 years old in last month.
It was the premier televised boxing event in the city since the passing of Hatton. As the last bell faded, the silence became a chant of "there's only one Hatton".
The competition inside the ropes reflected the emotion. Arthur was sent to the canvas by a powerful punch squarely on the face in the second round, standing uncertainly to his footing on the count of eight.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was injured early, heavy swelling developing under his face as the pair exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the pace seldom decreased over the full distance.
The victor narrowly won the decision with scoring tallies of draw, close margin and clearer margin, but both fighters were persistent and full of heart, all the qualities their idol Hatton stood for.
