UK light-heavyweight Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a majority decision in a close ten-round bout at the Co-op Live Arena.
But Parker had his moments, delivering effective single shots in a fight where the techniques failed to mesh, with constant grabbing spoiling the fight.
Two judges judged it 96-94 for to the winner, with the final judge a 95-95.
"It wasn't my best showing but what defines champions? They succeed," the victor stated in the arena as he was met by disapproval from the audience.
The Londoner bounced back after his first professional defeat - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Various analysts thought the challenger, 31, deserved the win but the British boxer endured the second loss of his 28-bout career.
Buatsi Claims Win in Slow Match
Buatsi's progress has plateaued in recent years through management issues and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to realize his potential - possibly in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with both competitors willing to take risks in a cagey initial rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was competing in only his second fight at the higher weight class.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who utilized a tight guard to narrowly win the cleaner periods.
The crowd's patience wore thin during frequent holding, with Parker slipping to the canvas various instances during grappling.
The underdog finished the stronger, but many rounds were difficult to score. Nevertheless, previous titleholder the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi advances, but with the caliber of hard hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Tribute Fuels Local Rivalry Fight
In the supporting bout, Arthur overcame Rea by divided decision in a outstanding local rivalry fight to secure the European light heavyweight title.
The venue became quiet for a extremely emotional homage before the fight as 10 bells sounded in memory of Manchester's own Hatton, who passed away aged 46 in last month.
It was the premier televised boxing event in the city since Hatton's passing. As the final chime ended, the quiet transitioned to a roar of "only one Hatton".
The action within the ring matched the sentiment. Arthur was knocked down by a left hook directly to the chin in the early round, rising shakily to his footing on the eight count.
But the traditional red shorts of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was marked up early, heavy swelling developing under his orbital area as the pair exchanged punishing blows.
Rea, 27, connected with strong blows but Arthur, 34, matched the intensity with powerful upward punches as the intensity rarely dropped over 12 rounds.
The victor narrowly won the result with official scores of draw, 115-113 and wider gap, but both fighters were relentless and brave, exactly what their hero Hatton represented.
