British light-heavyweight Buatsi secured a victory yet unimpressive start to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic medal winner's activity level likely gained him a split decision in a close 10-round contest at the Co-op Live Arena.
But Parker found success, connecting with powerful clean blows in a contest where the styles never quite clicked, with constant grabbing marring the action.
The scoring judges judged it 96-94 to the winner, with the third a even score.
"It wasn't my greatest display but how do champions respond? They prevail," Buatsi commented in the ringside as he was met by negative reactions from the spectators.
The Londoner got back to winning after his first professional defeat - an thrilling contest with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts thought Parker, thirty-one, deserved the win but the Derbyshire fighter endured the second setback of his 28-bout career.
Buatsi Claims Win in Dull Affair
Buatsi's progress has slowed in recent times through promotional disputes and considerable time of inactivity.
Once tipped as the next star of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what feels like a last chance - under new promotional backing.
He began cautiously, with both competitors willing to be aggressive in a calculated opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second fight at the higher weight class.
By the middle rounds, the underdog had made it competitive, causing problems for Buatsi, who utilized a protective stance to barely take the cleaner periods.
The spectators' acceptance wore thin because of regular grabbing, with the challenger slipping to the canvas multiple occasions during grappling.
Parker ended stronger, but multiple periods were hard to judge. However, previous titleholder Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Homage Inspires Local Rivalry Battle
In the secondary fight, Lyndon Arthur beat Bradley Rea by close verdict in a terrific local rivalry fight to win the European light-heavyweight belt.
The stadium became quiet for a extremely emotional homage ahead of the contest as ten bells rang in remembrance of local hero Hatton, who passed away at age 46 in last month.
It was the initial significant broadcast fight night in the urban center since Hatton's death. As the final chime disappeared, the quiet gave way to a roar of "there's just one Hatton".
The action during the bout equaled the feeling. Arthur was sent to the canvas by a left hook squarely on the chin in the initial stage, standing uncertainly to his feet on the eight count.
But the Manchester United-red attire of the fighter soon advanced again. Across the ring, the opponent - in rival City blue - was injured quickly, significant bruising appearing under his eye as the duo traded punishing blows.
Rea, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace rarely dropped over 12 rounds.
Arthur edged the verdict with scoring tallies of 114-114, close margin and wider gap, but the two athletes were determined and courageous, all the qualities their hero Hatton represented.
