UK light-heavyweight Buatsi secured a victory yet unimpressive start to life under new promoters with a decision win over Zach Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a close ten-round contest at the Manchester venue.
But Parker landed significant shots, connecting with powerful clean blows in a fight where the styles didn't complement each other, with constant grabbing disrupting the action.
Two judges had it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my best showing but how do champions respond? They prevail," the victor said in the arena as he was met by boos from the crowd.
The Londoner returned to winning ways after his first professional defeat - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Various analysts believed the challenger, 31, should have been awarded the decision but the British boxer suffered the second setback of his 28-bout career.
Buatsi Secures Triumph in Uneventful Encounter
Buatsi's progress has plateaued in recent times through contract problems and long spells of inactivity.
Once tipped as the next star of the British fight scene, he now finds himself trying to realize his potential - maybe in what seems like a final roll of the dice - under fresh management.
He began cautiously, with both competitors ready to take risks in a tentative early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was making just his second bout at the higher weight class.
By the middle rounds, the underdog had kept it close, causing problems for Buatsi, who operated with a tight guard to narrowly win the more effective periods.
The spectators' acceptance diminished during frequent holding, with Parker slipping to the canvas several times during close exchanges.
Parker finished the stronger, but many rounds were difficult to score. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, giving Buatsi just a single round.
Buatsi progresses, but with the caliber of power puncher David Benavidez, and Russian champion Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Memorial Inspires Manchester Derby Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by divided decision in a terrific Manchester vs Manchester fight to secure the European light heavyweight championship.
The venue became quiet for a deeply poignant tribute before the fight as ten bells sounded in honor of Manchester's own Ricky Hatton, who died 46 years old in recently.
It was the premier televised boxing event in the city since Hatton's death. As the final chime disappeared, the quiet transitioned to a chant of "there's only one Hatton".
The action during the bout equaled the sentiment. Arthur was floored by a powerful punch directly to the face in the initial stage, rising shakily to his position on the referee's count.
But the Manchester United-red attire of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was damaged quickly, noticeable damage appearing under his orbital area as the fighters exchanged powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the intensity hardly diminished over 12 rounds.
The victor barely secured the verdict with official scores of even score, narrow lead and clearer margin, but both fighters were determined and courageous, all the qualities their inspiration Hatton represented.
