British light heavyweight Buatsi earned a win yet disappointing beginning to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a close ten-round bout at the boxing arena.
But Parker had his moments, connecting with powerful single shots in a match where the styles failed to mesh, with constant grabbing marring the action.
The scoring judges judged it 96-94 to the winner, with the remaining official a even score.
"It wasn't my greatest showing but what defines champions? They win," the victor stated in the ring as he was met by disapproval from the audience.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to secure a 20th career victory.
Several boxing experts believed Parker, 31, should have been awarded the decision but the British boxer suffered the second loss of his 28-match professional journey.
Buatsi Secures Victory in Slow Affair
Buatsi's progress has plateaued in recent years through promotional disputes and long spells of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to achieve expectations - maybe in what feels like a last chance - under recent support.
He started carefully, with neither fighter ready to be aggressive in a calculated initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who utilized a protective stance to narrowly win the better stanzas.
The crowd's patience decreased because of constant clinching, with Parker slipping to the canvas various instances during clinches.
Parker closed well, but several stanzas were challenging to assess. However, previous titleholder Carl Frampton - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the presence of hard hitter David Benavidez, and Russian champion Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Homage Inspires Local Rivalry Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific local rivalry battle to capture the European light heavyweight championship.
The venue grew hushed for a extremely emotional memorial prior to the bout as 10 bells sounded in remembrance of Manchester's own Ricky Hatton, who died 46 years old in recently.
It was the initial significant broadcast match card in the city since Hatton's passing. As the concluding sound ended, the quiet gave way to a shout of "only one Hatton".
The competition within the ring reflected the feeling. The eventual winner was knocked down by a powerful punch squarely on the face in the initial stage, standing uncertainly to his footing on the eight count.
But the red-colored equipment of the fighter soon came forward again. On the opposite side, the opponent - in rival City blue - was damaged soon, noticeable damage developing under his orbital area as the fighters exchanged punishing blows.
Rea, 27, landed power punches but Arthur, 34, responded in kind with stinging uppercuts as the pace rarely dropped over 12 rounds.
The victor edged the result with judges scorecards of even score, close margin and wider gap, but the two athletes were persistent and full of heart, exactly what their inspiration Hatton embodied.
