British light-heavyweight Buatsi secured a victory yet underwhelming start to life under fresh promotional backing with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a majority decision in a close ten-round contest at the Co-op Live Arena.
But Parker had his moments, landing some telling single shots in a contest where the styles didn't complement each other, with constant grabbing disrupting the fight.
Two judges scored it 96-94 for to Buatsi, with the third a even score.
"It wasn't my finest display but what defines champions? They win," the victor stated in the arena as he was greeted with disapproval from the audience.
The Londoner got back to winning after his initial pro loss - an thrilling contest with Callum Smith in February - to claim a 20th pro success.
Various analysts thought Parker, 31, should have been awarded the win but the Derbyshire fighter suffered the second defeat of his 28-match career.
Buatsi Earns Victory in Dull Affair
His career development has plateaued in recent years through promotional disputes and considerable time of lack of fights.
Earlier forecast as the next star of UK boxing, he now is positioned trying to realize his potential - maybe in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers willing to take risks in a tentative initial rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was participating in his second bout at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a protective stance to narrowly win the cleaner stanzas.
The audience's tolerance decreased amid frequent holding, with the challenger falling to the floor multiple occasions during close exchanges.
Parker finished the stronger, but many rounds were hard to judge. Nevertheless, former world champion Carl Frampton - working with Dazn - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Motivates Local Rivalry Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a excellent Manchester vs Manchester fight to win the continental belt.
The arena fell silent for a deeply poignant memorial before the fight as a bell ceremony sounded in memory of the city's native Ricky Hatton, who passed away aged 46 in last month.
It was the first major televised fight night in the city since Hatton's passing. As the final chime disappeared, the stillness became a shout of "there's only one Ricky Hatton".
The action within the ring reflected the emotion. Arthur was knocked down by a significant blow directly to the face in the early round, rising shakily to his feet on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. Across the ring, the opponent - in competitive blue - was injured early, noticeable damage developing under his eye as the duo traded hard punches.
The challenger, 27, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the pace hardly diminished over the full distance.
Arthur barely secured the verdict with judges scorecards of even score, close margin and wider gap, but the two athletes were determined and courageous, all the qualities their idol the legend represented.
