UK light heavyweight Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But Parker landed significant shots, connecting with powerful single shots in a match where the styles failed to mesh, with frequent clinching spoiling the fight.
The officials scored it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my greatest display but what defines champions? They win," Buatsi commented in the arena as he was faced negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Various analysts thought Parker, thirty-one, should have been awarded the win but the contender suffered the second setback of his 28-match career.
Buatsi Earns Triumph in Slow Encounter
Buatsi's progress has plateaued in the past few years through promotional disputes and extended periods of lack of fights.
Previously predicted as the rising talent of UK boxing, he now stands trying to achieve expectations - perhaps in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers willing to take risks in a tentative initial rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was making just his second fight at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a protective stance to edge the more effective rounds.
The crowd's patience decreased amid regular grabbing, with Parker slipping to the canvas various instances during clinches.
Parker closed well, but many rounds were hard to judge. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - judging by this showing - still seems difficult.
Hatton Memorial Motivates All-Manchester Contest
In the co-main event, Lyndon Arthur beat Rea by divided decision in a outstanding Manchester vs Manchester battle to capture the continental championship.
The arena became quiet for a deeply poignant homage before the fight as ten bells tolled in remembrance of Manchester's own Hatton, who passed away aged 46 in September.
It was the premier televised match card in the urban center since Hatton's passing. As the final chime disappeared, the silence transitioned to a roar of "there's only one Ricky Hatton".
The action inside the ropes equaled the sentiment. The eventual winner was knocked down by a left hook squarely on the jaw in the initial stage, getting up unsteadily to his feet on the eight count.
But the red-colored attire of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was damaged quickly, noticeable damage forming under his orbital area as the duo landed hard punches.
The challenger, 27, connected with strong blows but the champion, 34, fought fire with fire with effective uppercuts as the pace rarely dropped over the full distance.
The victor narrowly won the decision with official scores of even score, close margin and 115-112, but each competitor were relentless and full of heart, everything their inspiration Hatton stood for.
