British light-heavyweight Buatsi secured a victory yet underwhelming beginning to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a tight ten-round fight at the boxing arena.
But the challenger found success, delivering effective single shots in a fight where the techniques never quite clicked, with constant grabbing disrupting the action.
The scoring judges had it 96-94 to the winner, with the final judge a even score.
"It wasn't my best performance but what defines champions? They prevail," the victor commented in the arena as he was greeted with boos from the crowd.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to secure a twentieth professional win.
Several boxing experts felt the challenger, thirty-one, deserved the decision but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
Buatsi Secures Win in Dull Encounter
Buatsi's progress has slowed in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with neither fighter willing to take risks in a cagey initial rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in 2022 after breaking his hand during the bout, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who utilized a solid defense to edge the cleaner periods.
The spectators' acceptance decreased during constant clinching, with Parker going down various instances during clinches.
The underdog ended stronger, but many rounds were difficult to score. Although, ex-champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the caliber of hard hitter Benavidez, and Russian star Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Memorial Fuels Local Rivalry Battle
In the co-main event, Arthur beat Bradley Rea by divided decision in a excellent Manchester vs Manchester contest to secure the continental belt.
The venue became quiet for a profoundly moving homage prior to the bout as 10 bells rang in memory of local hero Hatton, who succumbed at age 46 in recently.
It was the premier televised match card in the location since the passing of Hatton. As the final chime ended, the quiet gave way to a shout of "only one Ricky Hatton".
The action during the bout equaled the sentiment. Arthur was floored by a left hook squarely on the chin in the initial stage, rising shakily to his feet on the referee's count.
But the traditional red shorts of the fighter soon came forward again. On the opposite side, the opponent - in competitive blue - was marked up soon, significant bruising appearing under his orbital area as the pair traded hard punches.
The challenger, 27, connected with strong blows but the champion, 34, fought fire with fire with effective uppercuts as the intensity seldom decreased over 12 rounds.
The victor narrowly won the result with judges scorecards of even score, narrow lead and clearer margin, but the two athletes were relentless and full of heart, all the qualities their hero Hatton represented.
