UK light-heavyweight Buatsi secured a victory yet underwhelming beginning to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive ten-round fight at the boxing arena.
But Parker found success, landing some telling individual punches in a contest where the techniques failed to mesh, with frequent clinching disrupting the fight.
Two judges scored it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my best performance but how do champions respond? They prevail," Buatsi commented in the ring as he was faced boos from the crowd.
The British fighter bounced back after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a twentieth professional win.
Some ringside observers felt the challenger, thirty-one, merited the decision but the British boxer suffered the second defeat of his 28-bout career.
Buatsi Secures Victory in Uneventful Match
Buatsi's progress has stalled in recent times through management issues and considerable time of inactivity.
Once tipped as the next star of British boxing, he now is positioned trying to realize his potential - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors ready to take risks in a calculated early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand mid-fight, was competing in only his second bout at light-heavyweight.
By the halfway stage, Parker had kept it close, causing problems for Buatsi, who utilized a solid defense to barely take the cleaner rounds.
The crowd's patience decreased during regular grabbing, with the challenger going down several times during close exchanges.
The underdog finished the stronger, but several stanzas were difficult to score. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the presence of power puncher David Benavidez, and Russian champion Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Hatton Homage Inspires Manchester Derby Battle
In the co-main event, Arthur overcame Rea by divided decision in a excellent Manchester vs Manchester fight to win the continental title.
The stadium fell silent for a deeply poignant tribute ahead of the contest as 10 bells sounded in remembrance of the city's native Hatton, who passed away at age 46 in September.
It was the initial significant broadcast fight night in the location since Hatton's death. As the last bell faded, the quiet transitioned to a chant of "there's just one Hatton".
The action within the ring matched the feeling. The eventual winner was floored by a powerful punch directly to the jaw in the early round, rising shakily to his footing on the referee's count.
But the Manchester United-red shorts of the fighter soon came forward again. On the opposite side, the opponent - in competitive blue - was injured early, heavy swelling forming under his orbital area as the duo landed punishing blows.
Rea, twenty-seven, landed power punches but Arthur, 34, responded in kind with effective uppercuts as the pace seldom decreased over 12 rounds.
The victor edged the verdict with judges scorecards of draw, narrow lead and wider gap, but both fighters were determined and full of heart, everything their inspiration the legend stood for.
