British light-heavyweight Buatsi earned a win yet unimpressive start to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a tight 10-round contest at the Manchester venue.
But Parker found success, connecting with powerful clean blows in a match where the techniques didn't complement each other, with excessive holding marring the fight.
The officials judged it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my best display but what defines champions? They win," Buatsi commented in the ringside as he was faced boos from the audience.
The British fighter got back to winning after his initial pro loss - an epic battle with his previous opponent in last winter - to secure a twentieth professional win.
Some ringside observers felt Parker, thirty-one, deserved the win but the British boxer experienced the second loss of his 28-match professional journey.
The Champion Claims Victory in Uneventful Match
Buatsi's progress has stalled in recent years through contract problems and long spells of inactivity.
Once tipped as the next star of British boxing, he now stands trying to realize his potential - perhaps in what feels like a final roll of the dice - under recent support.
He began cautiously, with neither fighter willing to overcommit in a tentative early stages.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was participating in his second fight at light-heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who operated with a solid defense to narrowly win the cleaner stanzas.
The spectators' acceptance diminished amid frequent holding, with Parker falling to the floor multiple occasions during close exchanges.
Parker finished the stronger, but several stanzas were challenging to assess. Although, ex-champion Carl Frampton - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor advances, but with the likes of heavy hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Fuels All-Manchester Fight
In the co-main event, Lyndon Arthur defeated Rea by divided decision in a terrific Manchester vs Manchester battle to win the European light heavyweight belt.
The stadium fell silent for a profoundly moving tribute prior to the bout as 10 bells rang in honor of local hero Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the final chime disappeared, the silence transitioned to a roar of "there's just one Ricky Hatton".
The fighting within the ring equaled the sentiment. The eventual winner was knocked down by a powerful punch flush on the face in the early round, standing uncertainly to his position on the referee's count.
But the traditional red equipment of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was damaged quickly, significant bruising developing under his orbital area as the pair exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with stinging uppercuts as the pace rarely dropped over the full distance.
Arthur barely secured the decision with judges scorecards of 114-114, close margin and wider gap, but both fighters were determined and full of heart, all the qualities their idol Hatton embodied.
