UK light-heavyweight Buatsi secured a victory yet disappointing start to life under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close ten-round contest at the Manchester venue.
But Parker landed significant shots, landing some telling clean blows in a contest where the approaches never quite clicked, with constant grabbing marring the action.
The scoring judges had it 96-94 for to the winner, with the third a even score.
"It wasn't my finest display but what defines champions? They succeed," Buatsi said in the arena as he was met by boos from the audience.
The Londoner bounced back after his first professional defeat - an memorable fight with Callum Smith in last winter - to earn a twentieth professional win.
Several boxing experts thought the challenger, 31, merited the decision but the Derbyshire fighter experienced the second loss of his 28-fight professional journey.
Buatsi Secures Win in Uneventful Affair
Buatsi's progress has stalled in the past few years through promotional disputes and extended periods of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to realize his potential - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers prepared to overcommit in a cagey opening few rounds.
The challenger, whose sole prior loss 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 light-heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for Buatsi, who worked behind a tight guard to narrowly win the better rounds.
The audience's tolerance diminished because of frequent holding, with Parker going down several times during close exchanges.
The underdog finished the stronger, but several stanzas were hard to judge. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Inspires Local Rivalry Fight
In the secondary fight, Lyndon Arthur overcame Rea by divided decision in a terrific all-Manchester contest to win the continental championship.
The stadium grew hushed for a profoundly moving memorial ahead of the contest as ten bells rang in remembrance of local hero Hatton, who died at age 46 in recently.
It was the first major televised boxing event in the location since Hatton's death. As the last bell disappeared, the quiet gave way to a chant of "there's just one Hatton".
The competition during the bout matched the emotion. Arthur was knocked down by a left hook flush on the chin in the early round, getting up unsteadily to his footing on the count of eight.
But the Manchester United-red shorts of Arthur soon came forward again. Across the ring, the opponent - in rival City blue - was damaged early, significant bruising developing under his face as the fighters traded punishing blows.
Rea, 27, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the intensity hardly diminished over twelve rounds.
The victor barely secured the verdict with scoring tallies of draw, 115-113 and 115-112, but each competitor were persistent and courageous, exactly what their idol the legend represented.
