UK light heavyweight Buatsi earned a win yet underwhelming beginning to life under fresh promotional backing with a points victory over Zach Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close ten-round bout at the boxing arena.
But the challenger landed significant shots, landing some telling single shots in a fight where the styles didn't complement each other, with frequent clinching marring the fight.
Two judges judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my best display but what defines champions? They prevail," Buatsi said in the ring as he was faced boos from the crowd.
The Londoner returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to earn a 20th career victory.
Several boxing experts felt the challenger, 31, deserved the victory but the Derbyshire fighter experienced the second defeat of his 28-bout professional journey.
Buatsi Secures Win in Slow Encounter
Buatsi's progress has slowed in the past few years through contract problems and long spells of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to realize his potential - possibly in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with neither fighter ready to overcommit in a cagey early stages.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after suffering a hand injury in the contest, was participating in his second fight at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who worked behind a protective stance to barely take the cleaner stanzas.
The audience's tolerance diminished because of frequent holding, with the challenger falling to the floor several times during clinches.
The underdog ended stronger, but multiple periods were hard to judge. However, former world champion the boxing analyst - working with Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Russian champion Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Memorial Motivates Manchester Derby Contest
In the supporting bout, Lyndon Arthur overcame Rea by divided decision in a excellent local rivalry battle to capture the European light heavyweight belt.
The stadium grew hushed for a deeply poignant memorial ahead of the contest as a bell ceremony rang in honor of local hero Ricky Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the last bell faded, the stillness gave way to a shout of "there's just one Ricky Hatton".
The action during the bout equaled the sentiment. Arthur was knocked down by a significant blow directly to the face in the second round, rising shakily to his feet on the eight count.
But the Manchester United-red attire of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was marked up early, significant bruising appearing under his eye as the pair traded hard punches.
Rea, twenty-seven, landed power punches but Arthur, 34, responded in kind with stinging uppercuts as the pace hardly diminished over the full distance.
The victor edged the verdict with scoring tallies of even score, close margin and wider gap, but each competitor were determined and full of heart, exactly what their hero the legend stood for.
