UK light-heavyweight Buatsi earned a win yet underwhelming start to life under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a tight ten-round bout at the Manchester venue.
But Parker found success, landing some telling individual punches in a match where the styles didn't complement each other, with constant grabbing disrupting the contest.
The scoring judges scored it 96-94 to the winner, with the remaining official a even score.
"It wasn't my best display but how do champions respond? They prevail," Buatsi commented in the arena as he was greeted with boos from the spectators.
The Londoner returned to winning ways after his first professional defeat - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts thought the challenger, thirty-one, deserved the victory but the Derbyshire fighter experienced the second defeat of his 28-match career.
The Champion Secures Triumph in Slow Affair
His career development has stalled in recent times through management issues and extended periods of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to achieve expectations - possibly in what feels like a ultimate opportunity - under recent support.
He started carefully, with the two boxers prepared to overcommit in a cagey early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was participating in his second appearance at the higher weight class.
By the middle rounds, the underdog had made it competitive, creating difficulties for the favorite, who operated with a protective stance to edge the more effective periods.
The crowd's patience diminished amid constant clinching, with Parker going down multiple occasions during grappling.
Parker finished the stronger, but many rounds were hard to judge. Nevertheless, ex-champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Homage Inspires All-Manchester Fight
In the supporting bout, Arthur beat Rea by close verdict in a excellent Manchester vs Manchester battle to secure the European light heavyweight championship.
The stadium became quiet for a deeply poignant homage prior to the bout as ten bells sounded in remembrance of Manchester's own Ricky Hatton, who succumbed at age 46 in recently.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the final chime disappeared, the quiet transitioned to a chant of "only one Hatton".
The competition during the bout matched the sentiment. The eventual winner was floored by a significant blow flush on the chin in the second round, getting up unsteadily to his position on the count of eight.
But the traditional red attire of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was injured quickly, noticeable damage developing under his orbital area as the fighters exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with effective uppercuts as the pace rarely dropped over the full distance.
Arthur barely secured the result with scoring tallies of draw, narrow lead and wider gap, but both fighters were persistent and courageous, all the qualities their inspiration Hatton stood for.
