British light-heavyweight Buatsi secured a victory yet underwhelming beginning to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a majority decision in a tight ten-round bout at the Manchester venue.
But Parker landed significant shots, landing some telling single shots in a match where the approaches didn't complement each other, with excessive holding disrupting the contest.
The officials judged it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my greatest showing but what defines champions? They win," the victor said in the ringside as he was met by negative reactions from the crowd.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to earn a 20th pro success.
Several boxing experts believed Parker, thirty-one, merited the win but the Derbyshire fighter endured the second setback of his 28-match professional journey.
Buatsi Secures Win in Dull Match
His career development has slowed in recent times through contract problems and considerable time of lack of fights.
Earlier forecast as the future of the British fight scene, he now finds himself trying to achieve expectations - possibly in what seems like a ultimate opportunity - under recent support.
He began cautiously, with neither fighter prepared to overcommit in a tentative initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who operated with a solid defense to edge the more effective periods.
The crowd's patience wore thin because of constant clinching, with Parker slipping to the canvas several times during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. However, ex-champion Carl Frampton - working with Dazn - had it strongly leaning for Parker, giving Buatsi just one round.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian star Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Homage Motivates Manchester Derby Contest
In the co-main event, Lyndon Arthur beat Rea by close verdict in a terrific all-Manchester fight to capture the European light heavyweight championship.
The stadium grew hushed for a deeply poignant tribute prior to the bout as ten bells tolled in honor of Manchester's own Ricky Hatton, who passed away aged 46 in September.
It was the first major televised match card in the urban center since Hatton's death. As the concluding sound ended, the quiet transitioned to a chant of "only one Ricky Hatton".
The fighting during the bout matched the sentiment. The eventual winner was floored by a left hook squarely on the jaw in the early round, standing uncertainly to his footing on the eight count.
But the traditional red attire of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was damaged quickly, heavy swelling forming under his eye as the fighters traded hard punches.
Rea, 27, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the action seldom decreased over 12 rounds.
The victor barely secured the result with scoring tallies of 114-114, narrow lead and clearer margin, but both fighters were determined and full of heart, everything their hero the legend embodied.
