UK light-heavyweight Buatsi earned a win yet disappointing beginning to his career under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a split decision in a close 10-round bout at the boxing arena.
But the challenger landed significant shots, connecting with powerful clean blows in a fight where the approaches never quite clicked, with frequent clinching marring the action.
The scoring judges had it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest performance but how do champions respond? They win," Buatsi said in the ringside as he was greeted with disapproval from the audience.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to earn a 20th career victory.
Several boxing experts believed the challenger, 31, deserved the victory but the Derbyshire fighter experienced the second defeat of his 28-match career.
The Champion Secures Victory in Slow Match
His career development has plateaued in recent times through promotional disputes and long spells of inactivity.
Earlier forecast as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what feels like a last chance - under recent support.
He began cautiously, with both competitors ready to take risks in a cagey opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after damaging his hand mid-fight, was making just his second fight at the higher weight class.
By the halfway stage, Parker had made it competitive, making life awkward for Buatsi, who operated with a protective stance to barely take the better periods.
The spectators' acceptance diminished because of regular grabbing, with Parker slipping to the canvas various instances during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. Although, previous titleholder Carl Frampton - working with Dazn - had it particularly wide for the challenger, scoring for Buatsi just a single round.
The victor progresses, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - on this evidence - still seems difficult.
Hatton Memorial Motivates Manchester Derby Fight
In the secondary fight, Lyndon Arthur beat Rea by split-decision in a excellent Manchester vs Manchester battle to win the continental championship.
The arena grew hushed for a profoundly moving homage before the fight as 10 bells tolled in honor of local hero Hatton, who succumbed aged 46 in last month.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the final chime faded, the quiet gave way to a chant of "there's just one Hatton".
The competition during the bout reflected the emotion. The eventual winner was floored by a left hook directly to the jaw in the early round, rising shakily to his footing on the referee's count.
But the red-colored equipment of Arthur soon came forward again. On the opposite side, Rea - in rival City blue - was damaged soon, noticeable damage appearing under his orbital area as the duo exchanged hard punches.
Rea, 27, connected with strong blows but Arthur, thirty-four, matched the intensity with stinging uppercuts as the pace hardly diminished over 12 rounds.
Arthur barely secured the verdict with official scores of 114-114, narrow lead and 115-112, but both fighters were determined and full of heart, all the qualities their hero Hatton stood for.
