UK light-heavyweight Buatsi earned a win yet disappointing start to life under fresh promotional backing with a points victory over Zach Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a close 10-round fight at the boxing arena.
But Parker had his moments, connecting with powerful individual punches in a fight where the approaches failed to mesh, with frequent clinching marring the contest.
The officials judged it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my best display but what defines champions? They win," the victor commented in the ringside as he was met by disapproval from the crowd.
The British fighter bounced back after his initial pro loss - an epic battle with Callum Smith in February - to earn a 20th career victory.
Some ringside observers felt the challenger, 31, deserved the decision but the British boxer experienced the second loss of his 28-fight career.
The Champion Claims Triumph in Dull Affair
His career development has stalled in recent years through contract problems and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers prepared to overcommit in a tentative initial rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after suffering a hand injury 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 utilized a tight guard to narrowly win the cleaner rounds.
The crowd's patience wore thin because of frequent holding, with Parker falling to the floor several times during grappling.
Parker finished the stronger, but many rounds were hard to judge. Nevertheless, previous titleholder the boxing analyst - working with Dazn - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor moves on, but with the caliber of power puncher David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Memorial Fuels All-Manchester Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester contest to secure the European light-heavyweight championship.
The arena grew hushed for a extremely emotional tribute ahead of the contest as a bell ceremony sounded in remembrance of the city's native Ricky Hatton, who died 46 years old in recently.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the final chime faded, the stillness transitioned to a roar of "there's only one Ricky Hatton".
The competition during the bout equaled the sentiment. The eventual winner was sent to the canvas by a powerful punch squarely on the jaw in the early round, standing uncertainly to his position on the referee's count.
But the traditional red shorts of Arthur soon advanced again. On the opposite side, Rea - in competitive blue - was injured soon, significant bruising appearing under his face as the pair traded powerful shots.
Rea, 27, landed power punches but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action seldom decreased over twelve rounds.
The victor edged the verdict with official scores of even score, 115-113 and clearer margin, but the two athletes were persistent and brave, everything their hero Hatton embodied.
