UK light-heavyweight Buatsi made a winning yet unimpressive debut to life under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a competitive ten-round fight at the Manchester venue.
But Parker had his moments, delivering effective clean blows in a contest where the approaches didn't complement each other, with constant grabbing spoiling the fight.
Two judges scored it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best showing but what defines champions? They win," Buatsi commented in the ringside as he was faced negative reactions from the spectators.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in February - to secure a 20th pro success.
Several boxing experts believed Parker, thirty-one, should have been awarded the win but the Derbyshire fighter suffered the second setback of his 28-fight professional journey.
Buatsi Secures Triumph in Uneventful Affair
His career development has slowed in recent years through management issues and considerable time of inactivity.
Earlier forecast as the rising talent of British boxing, he now stands trying to realize his potential - possibly in what seems like a final roll of the dice - under recent support.
He began cautiously, with the two boxers ready to take risks in a calculated initial rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after breaking his hand during the bout, was competing in only his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, creating difficulties for Buatsi, who utilized a protective stance to narrowly win the better periods.
The spectators' acceptance wore thin amid frequent holding, with the challenger slipping to the canvas several times during close exchanges.
Parker ended stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a excellent all-Manchester contest to capture the European light-heavyweight belt.
The stadium fell silent for a deeply poignant memorial before the fight as a bell ceremony tolled in remembrance of the city's native Hatton, who succumbed 46 years old in recently.
It was the first major televised match card in the urban center since Hatton's death. As the final chime faded, the stillness transitioned to a roar of "there's just one Ricky Hatton".
The fighting inside the ropes equaled the emotion. The eventual winner was knocked down by a significant blow flush on the jaw in the second round, getting up unsteadily to his feet on the count of eight.
But the red-colored attire of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was injured early, noticeable damage forming under his eye as the duo exchanged powerful shots.
Rea, 27, connected with strong blows but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity hardly diminished over twelve rounds.
Arthur narrowly won the result with scoring tallies of 114-114, narrow lead and 115-112, but both fighters were determined and full of heart, everything their inspiration the legend embodied.
