UK light-heavyweight Buatsi earned a win yet disappointing debut to his career under new promoters with a points victory over Zach Parker in Manchester.
The Olympic medal winner's work rate likely gained him a judges' verdict in a competitive ten-round contest at the boxing arena.
But Parker had his moments, landing some telling individual punches in a match where the techniques didn't complement each other, with excessive holding spoiling the action.
Two judges judged it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They win," the victor said in the ringside as he was greeted with negative reactions from the crowd.
The Londoner bounced back after his first professional defeat - an thrilling contest with Callum Smith in February - to claim a 20th pro success.
Some ringside observers felt Parker, 31, deserved the victory but the Derbyshire fighter endured the second setback of his 28-match professional journey.
Buatsi Claims Triumph in Slow Encounter
His career development has stalled in recent times through contract problems 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 seems like a last chance - under fresh management.
He began cautiously, with neither fighter willing to overcommit in a calculated early stages.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand mid-fight, was making just his second appearance at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who operated with a protective stance to edge the better stanzas.
The spectators' acceptance diminished amid frequent holding, with Parker slipping to the canvas several times during grappling.
Parker finished the stronger, but several stanzas were hard to judge. Nevertheless, ex-champion Carl Frampton - working with Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
Buatsi progresses, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Hatton Memorial Fuels All-Manchester Fight
In the secondary fight, Lyndon Arthur defeated Bradley Rea by split-decision in a excellent local rivalry contest to secure the continental title.
The venue fell silent for a deeply poignant memorial before the fight as ten bells rang in honor of the city's native Hatton, who succumbed aged 46 in recently.
It was the first major televised boxing event in the location since the passing of Hatton. As the final chime disappeared, the silence transitioned to a shout of "only one Ricky Hatton".
The fighting during the bout reflected the sentiment. The eventual winner was knocked down by a powerful punch directly to the face in the second round, standing uncertainly to his feet on the count of eight.
But the red-colored shorts of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was damaged quickly, noticeable damage forming under his orbital area as the duo exchanged powerful shots.
The challenger, 27, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the pace rarely dropped over twelve rounds.
Arthur narrowly won the decision with judges scorecards of draw, close margin and 115-112, but each competitor were persistent and full of heart, all the qualities their idol Hatton represented.
