UK light-heavyweight Buatsi secured a victory yet disappointing debut to his career under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's punch output likely gained him a judges' verdict in a tight 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful single shots in a fight where the approaches didn't complement each other, with excessive holding disrupting the action.
Two judges scored it 96-94 for to the winner, with the third a 95-95.
"It wasn't my finest showing but what defines champions? They win," Buatsi commented in the ring as he was met by disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in February - to claim a 20th career victory.
Some ringside observers thought the challenger, thirty-one, deserved the win but the British boxer suffered the second setback of his 28-bout professional journey.
The Champion Earns Triumph in Dull Encounter
The fighter's advancement has slowed in recent years through management issues and considerable time of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors willing to overcommit in a tentative early stages.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was making just his second appearance at the higher weight class.
By the fight's midpoint, the underdog had kept it close, causing problems for Buatsi, who worked behind a tight guard to edge the more effective periods.
The crowd's patience diminished because of constant clinching, with Parker slipping to the canvas several times during clinches.
Parker ended stronger, but multiple periods were difficult to score. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for Parker, giving Buatsi just one round.
Buatsi progresses, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Tribute Inspires Manchester Derby Contest
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a terrific all-Manchester contest to capture the European light heavyweight belt.
The arena became quiet for a extremely emotional homage before the fight as 10 bells rang in memory of local hero Hatton, who passed away aged 46 in recently.
It was the first major televised match card in the city since Hatton's passing. As the final chime ended, the quiet gave way to a shout of "there's just one Hatton".
The fighting within the ring reflected the feeling. Arthur was floored by a significant blow flush on the face in the second round, standing uncertainly to his footing on the count of eight.
But the traditional red equipment of Arthur soon came forward again. On the opposite side, the opponent - in opposing blue - was damaged quickly, noticeable damage forming under his orbital area as the duo landed powerful shots.
The challenger, twenty-seven, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the action rarely dropped over twelve rounds.
The victor narrowly won the decision with official scores of draw, narrow lead and wider gap, but the two athletes were relentless and brave, all the qualities their inspiration Hatton stood for.
