UK light heavyweight Buatsi earned a win yet unimpressive start to life under new promoters with a decision win over Zach Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a competitive 10-round fight at the Manchester venue.
But the challenger landed significant shots, delivering effective single shots in a fight where the techniques didn't complement each other, with frequent clinching marring the action.
The officials had it 96-94 to Buatsi, with the final judge a 95-95.
"It wasn't my best display but how do champions respond? They prevail," Buatsi stated in the ring as he was faced boos from the audience.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers felt the challenger, thirty-one, deserved the decision but the Derbyshire fighter endured the second defeat of his 28-bout career.
The Champion Claims Win in Uneventful Affair
Buatsi's progress has slowed in recent times through promotional disputes and long spells of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to realize his potential - maybe in what seems like a last chance - under new promotional backing.
He started carefully, with the two boxers ready to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second fight at the higher weight class.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who operated with a protective stance to narrowly win the better stanzas.
The audience's tolerance diminished because of regular grabbing, with the challenger slipping to the canvas several times during clinches.
The underdog finished the stronger, but several stanzas were challenging to assess. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just a single round.
The victor moves on, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
Hatton Homage Motivates All-Manchester Contest
In the secondary fight, Lyndon Arthur overcame Rea by close verdict in a terrific all-Manchester fight to capture the European light-heavyweight belt.
The arena fell silent for a profoundly moving memorial prior to the bout as ten bells rang in remembrance of Manchester's own Hatton, who died at age 46 in recently.
It was the initial significant broadcast match card in the city since Hatton's death. As the final chime disappeared, the stillness gave way to a shout of "there's just one Hatton".
The action within the ring matched the sentiment. The eventual winner was floored by a significant blow squarely on the chin in the initial stage, standing uncertainly to his feet on the referee's count.
But the traditional red attire of Arthur soon advanced again. Across the ring, Rea - in rival City blue - was marked up quickly, significant bruising forming under his face as the fighters exchanged powerful shots.
Rea, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with stinging uppercuts as the action hardly diminished over the full distance.
Arthur narrowly won the decision with official scores of draw, narrow lead and clearer margin, but both fighters were determined and full of heart, exactly what their idol Hatton represented.
