British light-heavyweight Buatsi secured a victory yet underwhelming start to life under new promoters with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a split decision in a close 10-round bout at the Manchester venue.
But the challenger had his moments, landing some telling single shots in a fight where the styles failed to mesh, with frequent clinching spoiling the action.
Two judges had it 96-94 for to the winner, with the final judge a even score.
"It wasn't my best performance but what do champions do? They prevail," Buatsi commented in the arena as he was faced boos from the spectators.
The British fighter bounced back after his maiden career setback - an epic battle with Callum Smith in February - to claim a 20th pro success.
Several boxing experts felt the challenger, thirty-one, merited the decision but the British boxer experienced the second defeat of his 28-bout career.
Buatsi Secures Win in Dull Encounter
Buatsi's progress has plateaued in recent years through management issues and extended periods of lack of fights.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors ready to overcommit in a cagey initial rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after breaking his hand mid-fight, was making just his second bout at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for the favorite, who utilized a protective stance to barely take the better stanzas.
The audience's tolerance diminished during frequent holding, with Parker slipping to the canvas various instances during grappling.
Parker finished the stronger, but many rounds were hard to judge. Nevertheless, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the caliber of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Hatton Tribute Fuels All-Manchester Contest
In the secondary fight, Arthur beat Bradley Rea by close verdict in a outstanding local rivalry battle to secure the continental championship.
The arena grew hushed for a deeply poignant memorial prior to the bout as ten bells sounded in remembrance of Manchester's own Ricky Hatton, who died at age 46 in recently.
It was the first major televised boxing event in the city since Hatton's death. As the last bell faded, the quiet became a shout of "only one Hatton".
The fighting during the bout reflected the sentiment. The eventual winner was floored by a left hook directly to the jaw in the second round, standing uncertainly to his footing on the eight count.
But the red-colored attire of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was marked up early, significant bruising developing under his orbital area as the fighters traded hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the action seldom decreased over twelve rounds.
Arthur barely secured the verdict with scoring tallies of even score, close margin and wider gap, but both fighters were relentless and full of heart, everything their idol Hatton represented.
