British light heavyweight Buatsi earned a win yet underwhelming beginning to his career under new promoters with a points victory over Zach Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a tight ten-round bout at the Co-op Live Arena.
But Parker found success, connecting with powerful single shots in a match where the styles failed to mesh, with frequent clinching disrupting the action.
Two judges judged it 96-94 to the winner, with the final judge a even score.
"It wasn't my finest performance but how do champions respond? They succeed," the victor said in the ringside as he was faced negative reactions from the spectators.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Some ringside observers believed Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter experienced the second setback of his 28-match career.
The Champion Secures Triumph in Slow Encounter
Buatsi's progress has slowed in recent times through contract problems and long spells of lack of fights.
Previously predicted as the next star of UK boxing, he now stands trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with the two boxers ready to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second bout at the higher weight class.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who worked behind a solid defense to edge the better stanzas.
The crowd's patience wore thin amid regular grabbing, with Parker falling to the floor various instances during close exchanges.
Parker closed well, but several stanzas were challenging to assess. However, ex-champion Carl Frampton - working with Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the likes of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Memorial Motivates Local Rivalry Contest
In the supporting bout, Lyndon Arthur overcame Rea by divided decision in a terrific all-Manchester fight to win the European light-heavyweight belt.
The arena fell silent for a profoundly moving memorial before the fight as ten bells rang in honor of local hero Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the last bell faded, the stillness transitioned to a chant of "only one Ricky Hatton".
The competition during the bout matched the sentiment. The eventual winner was floored by a significant blow squarely on the jaw in the second round, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was injured soon, noticeable damage appearing under his face as the fighters landed punishing blows.
Rea, 27, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the intensity hardly diminished over twelve rounds.
The victor barely secured the decision with official scores of draw, 115-113 and 115-112, but the two athletes were persistent and courageous, all the qualities their idol Hatton stood for.
