UK light-heavyweight Buatsi made a winning yet disappointing debut to his career under fresh promotional backing with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a close ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful single shots in a match where the styles didn't complement each other, with constant grabbing disrupting the fight.
The officials scored it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my best performance but how do champions respond? They win," Buatsi commented in the arena as he was met by negative reactions from the crowd.
The Londoner got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Various analysts thought Parker, 31, deserved the win but the Derbyshire fighter experienced the second setback of his 28-bout professional journey.
The Champion Claims Victory in Slow Encounter
Buatsi's progress has stalled in the past few years through management issues and extended periods of inactivity.
Previously predicted as the rising talent of UK 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 the two boxers ready to overcommit in a calculated opening few rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was making just his second bout at the higher weight class.
By the halfway stage, Parker had stayed in contention, making life awkward for Buatsi, who worked behind a solid defense to narrowly win the better stanzas.
The crowd's patience decreased during constant clinching, with Parker slipping to the canvas various instances during close exchanges.
Parker closed well, but many rounds were hard to judge. However, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of hard hitter David Benavidez, and Russian champion Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Hatton Memorial Fuels All-Manchester Contest
In the supporting bout, Lyndon Arthur beat Rea by divided decision in a excellent Manchester vs Manchester battle to secure the continental belt.
The venue became quiet for a extremely emotional tribute ahead of the contest as a bell ceremony tolled in honor of the city's native Ricky Hatton, who died at age 46 in September.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the concluding sound disappeared, the quiet transitioned to a shout of "only one Hatton".
The competition during the bout matched the feeling. Arthur was knocked down by a significant blow flush on the jaw in the second round, standing uncertainly to his footing on the eight count.
But the traditional red shorts of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was marked up early, significant bruising appearing under his orbital area as the fighters landed powerful shots.
The challenger, 27, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over the full distance.
The victor barely secured the result with scoring tallies of draw, narrow lead and wider gap, but both fighters were determined and brave, everything their idol Hatton embodied.
