UK light heavyweight Buatsi made a winning yet unimpressive start to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a close 10-round contest at the boxing arena.
But Parker found success, connecting with powerful individual punches in a contest where the techniques never quite clicked, with frequent clinching disrupting the action.
The officials had it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my best showing but what do champions do? They prevail," the victor stated in the arena as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to earn a 20th pro success.
Various analysts thought Parker, thirty-one, should have been awarded the win but the Derbyshire fighter experienced the second setback of his 28-fight career.
The Champion Earns Win in Dull Encounter
His career development has plateaued in recent times through management issues and considerable time of inactivity.
Once tipped as the next star of British boxing, he now is positioned trying to achieve expectations - maybe in what feels like a last chance - under fresh management.
He started carefully, with neither fighter willing to take risks in a cagey opening few rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was competing in only his second bout at the higher weight class.
By the middle rounds, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a solid defense to narrowly win the better periods.
The audience's tolerance decreased amid frequent holding, with Parker going down various instances during grappling.
The underdog closed well, but several stanzas were difficult to score. Nevertheless, previous titleholder Carl Frampton - working with the broadcast network - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor progresses, but with the presence of power puncher David Benavidez, and Russian star Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Memorial Fuels Local Rivalry Contest
In the secondary fight, Arthur overcame Rea by split-decision in a terrific all-Manchester fight to win the European light-heavyweight championship.
The venue grew hushed for a profoundly moving homage prior to the bout as a bell ceremony tolled in remembrance of the city's native Hatton, who died at age 46 in September.
It was the premier televised boxing event in the location since the passing of Hatton. As the concluding sound ended, the silence gave way to a shout of "there's just one Ricky Hatton".
The fighting within the ring matched the sentiment. Arthur was knocked down by a left hook flush on the chin in the initial stage, rising shakily to his feet on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was damaged quickly, significant bruising developing under his eye as the pair landed hard punches.
The challenger, 27, landed power punches but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action hardly diminished over 12 rounds.
Arthur edged the verdict with official scores of 114-114, 115-113 and 115-112, but both fighters were determined and full of heart, everything their idol Hatton represented.
