British light heavyweight Buatsi made a winning yet unimpressive start to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a split decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger had his moments, delivering effective clean blows in a contest where the approaches never quite clicked, with excessive holding spoiling the fight.
The scoring judges judged it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my finest display but what do champions do? They succeed," Buatsi commented in the ringside as he was faced boos from the crowd.
The British fighter bounced back after his initial pro loss - an thrilling contest with Callum Smith in February - to claim a 20th pro success.
Several boxing experts thought the challenger, thirty-one, merited the decision but the British boxer suffered the second setback of his 28-match professional journey.
The Champion Earns Victory in Slow Match
Buatsi's progress has slowed in the past few years through management issues and extended periods of inactivity.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a last chance - under new promotional backing.
He opened tentatively, with neither fighter prepared to take risks in a calculated early stages.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after suffering a hand injury during the bout, was participating in his second fight at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who operated with a tight guard to edge the cleaner periods.
The audience's tolerance decreased because of regular grabbing, with the challenger falling to the floor several times during clinches.
The underdog ended stronger, but many rounds were difficult to score. However, ex-champion the boxing analyst - working with the broadcast network - had it significantly in favor for Parker, awarding Buatsi just a single round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Inspires All-Manchester Contest
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding local rivalry fight to win the continental title.
The venue fell silent for a profoundly moving tribute prior to the bout as ten bells sounded in memory of the city's native Hatton, who died at age 46 in last month.
It was the first major televised fight night in the city since Hatton's death. As the final chime faded, the stillness transitioned to a roar of "there's just one Ricky Hatton".
The competition inside the ropes equaled the feeling. Arthur was floored by a left hook flush on the face in the early round, getting up unsteadily to his footing on the referee's count.
But the traditional red equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in rival City blue - was injured soon, noticeable damage appearing under his orbital area as the duo exchanged hard punches.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with effective uppercuts as the intensity seldom decreased over the full distance.
Arthur edged the verdict with scoring tallies of even score, close margin and clearer margin, but both fighters were determined and courageous, all the qualities their inspiration Hatton embodied.
