UK light-heavyweight Buatsi earned a win yet disappointing start to life under new promoters with a points victory over Zach Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a competitive ten-round bout at the boxing arena.
But Parker had his moments, delivering effective clean blows in a contest where the approaches didn't complement each other, with excessive holding marring the contest.
The scoring judges judged it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my best display but what defines champions? They win," Buatsi said in the arena as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Some ringside observers felt Parker, 31, deserved the decision but the Derbyshire fighter suffered the second defeat of his 28-match career.
Buatsi Secures Win in Slow Affair
Buatsi's progress has slowed in recent times through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now stands trying to achieve expectations - possibly in what feels like a ultimate opportunity - under fresh management.
He opened tentatively, with the two boxers prepared to overcommit in a cagey opening few rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second fight at the higher weight class.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who utilized a protective stance to narrowly win the cleaner rounds.
The audience's tolerance decreased amid constant clinching, with the challenger going down several times during clinches.
The underdog closed well, but multiple periods were difficult to score. However, former world champion Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor advances, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the secondary fight, Lyndon Arthur beat Rea by close verdict in a terrific local rivalry battle to capture the European light heavyweight belt.
The venue grew hushed for a deeply poignant memorial prior to the bout as 10 bells rang in memory of Manchester's own Ricky Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the concluding sound faded, the silence gave way to a shout of "there's just one Ricky Hatton".
The competition during the bout equaled the feeling. The eventual winner was knocked down by a significant blow squarely on the jaw in the early round, standing uncertainly to his feet on the eight count.
But the Manchester United-red shorts of Arthur soon came forward again. From the other corner, Rea - in rival City blue - was marked up quickly, significant bruising developing under his face as the duo traded hard punches.
Rea, 27, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the intensity seldom decreased over 12 rounds.
Arthur edged the verdict with scoring tallies of even score, close margin and wider gap, but both fighters were relentless and full of heart, exactly what their inspiration Hatton stood for.
