UK light-heavyweight Buatsi made a winning yet underwhelming debut to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a close ten-round fight at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective clean blows in a match where the techniques didn't complement each other, with constant grabbing disrupting the action.
The scoring judges scored it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my finest display but how do champions respond? They succeed," Buatsi stated in the ringside as he was greeted with boos from the crowd.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in February - to earn a 20th career victory.
Several boxing experts believed Parker, 31, deserved the victory but the Derbyshire fighter suffered the second setback of his 28-fight career.
Buatsi Claims Win in Uneventful Affair
His career development has plateaued in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of the British fight scene, he now stands trying to realize his potential - possibly in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with the two boxers willing to take risks in a cagey early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand mid-fight, was making just his second appearance at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for the favorite, who operated with a solid defense to edge the more effective rounds.
The crowd's patience diminished during frequent holding, with Parker going down several times during clinches.
The underdog ended stronger, but many rounds were hard to judge. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the presence of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Hatton Tribute Motivates All-Manchester Fight
In the co-main event, Arthur overcame Rea by split-decision in a excellent local rivalry battle to capture the European light-heavyweight championship.
The stadium became quiet for a extremely emotional tribute ahead of the contest as a bell ceremony rang in honor of Manchester's own Ricky Hatton, who succumbed at age 46 in recently.
It was the premier televised boxing event in the location since Hatton's death. As the final chime disappeared, the silence gave way to a shout of "only one Ricky Hatton".
The competition during the bout reflected the emotion. The eventual winner was knocked down by a powerful punch directly to the face in the second round, getting up unsteadily to his footing on the eight count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. Across the ring, the opponent - in rival City blue - was marked up early, significant bruising forming under his face as the pair exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, responded in kind with effective uppercuts as the intensity seldom decreased over twelve rounds.
Arthur edged the decision with scoring tallies of even score, narrow lead and wider gap, but both fighters were relentless and full of heart, exactly what their hero Hatton represented.
