British light heavyweight Buatsi earned a win yet disappointing beginning to life under new promoters with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a close ten-round bout at the Manchester venue.
But Parker had his moments, connecting with powerful individual punches in a fight where the styles failed to mesh, with frequent clinching marring the fight.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my greatest showing but what do champions do? They prevail," Buatsi commented in the arena as he was met by negative reactions from the spectators.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Various analysts believed Parker, 31, should have been awarded the win but the British boxer experienced the second defeat of his 28-bout professional journey.
The Champion Earns Victory in Slow Affair
Buatsi's progress has stalled in the past few years through management issues and long spells of lack of fights.
Previously predicted as the future of British boxing, he now finds himself trying to realize his potential - maybe in what appears to be a last chance - under fresh management.
He opened tentatively, with neither fighter prepared to take risks in a tentative initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was participating in his second bout at light-heavyweight.
By the halfway stage, Parker had stayed in contention, making life awkward for the favorite, who operated with a protective stance to narrowly win the cleaner periods.
The spectators' acceptance diminished amid regular grabbing, with Parker going down multiple occasions during close exchanges.
Parker ended stronger, but several stanzas were hard to judge. Nevertheless, former world champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, awarding Buatsi just one round.
The victor advances, but with the presence of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Hatton Tribute Motivates Local Rivalry Fight
In the supporting bout, Arthur defeated Rea by divided decision in a terrific all-Manchester contest to capture the continental belt.
The venue fell silent for a profoundly moving homage before the fight as ten bells tolled in memory of the city's native Ricky Hatton, who succumbed aged 46 in recently.
It was the first major televised boxing event in the location since Hatton's passing. As the concluding sound disappeared, the quiet transitioned to a shout of "there's only one Ricky Hatton".
The action inside the ropes matched the emotion. The eventual winner was floored by a left hook directly to the face in the initial stage, standing uncertainly to his footing on the referee's count.
But the traditional red shorts of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was damaged early, significant bruising developing under his eye as the duo traded hard punches.
Rea, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the action seldom decreased over 12 rounds.
The victor barely secured the verdict with official scores of 114-114, 115-113 and clearer margin, but the two athletes were relentless and courageous, exactly what their inspiration Hatton stood for.
