UK light heavyweight Buatsi earned a win yet disappointing start to his career under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a competitive ten-round bout at the Manchester venue.
But the challenger had his moments, delivering effective clean blows in a match where the techniques never quite clicked, with constant grabbing spoiling the contest.
Two judges had it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my greatest performance but how do champions respond? They win," Buatsi stated in the ringside as he was met by negative reactions from the crowd.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Some ringside observers felt the challenger, thirty-one, merited the decision but the Derbyshire fighter experienced the second defeat of his 28-fight professional journey.
The Champion Earns Triumph in Uneventful Encounter
The fighter's advancement has slowed in the past few years through management issues and extended periods of inactivity.
Once tipped as the next star of British boxing, he now is positioned trying to realize his potential - possibly in what seems like a last chance - under recent support.
He opened tentatively, with neither fighter ready to overcommit 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 mid-fight, was making just his second fight at the higher weight class.
By the middle rounds, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to barely take the cleaner stanzas.
The crowd's patience diminished during frequent holding, with Parker going down various instances during grappling.
The underdog closed well, but several stanzas were hard to judge. Although, ex-champion Carl Frampton - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Russian champion Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Fight
In the supporting bout, Lyndon Arthur beat Rea by split-decision in a excellent local rivalry battle to win the European light heavyweight championship.
The arena grew hushed for a profoundly moving tribute before the fight as a bell ceremony tolled in honor of Manchester's own Hatton, who passed away at age 46 in recently.
It was the first major televised match card in the location since Hatton's passing. As the concluding sound ended, the quiet transitioned to a shout of "only one Hatton".
The fighting inside the ropes equaled the emotion. Arthur was knocked down by a left hook directly to the jaw in the second round, rising shakily to his position on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. Across the ring, Rea - in opposing blue - was damaged quickly, significant bruising appearing under his eye as the duo exchanged powerful shots.
Rea, 27, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the pace rarely dropped over twelve rounds.
The victor barely secured the verdict with judges scorecards of 114-114, narrow lead and 115-112, but the two athletes were persistent and brave, all the qualities their inspiration the legend embodied.
