British light-heavyweight Buatsi made a winning yet underwhelming start to his career under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a competitive ten-round bout at the Co-op Live Arena.
But the challenger had his moments, landing some telling clean blows in a contest where the styles didn't complement each other, with frequent clinching disrupting the fight.
The officials scored it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my best display but what do champions do? They prevail," the victor said in the ring as he was faced negative reactions from the crowd.
The Londoner bounced back after his maiden career setback - an thrilling contest with his previous opponent in last winter - to claim a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, deserved the decision but the Derbyshire fighter experienced the second setback of his 28-match professional journey.
The Champion Claims Victory in Slow Encounter
His career development has plateaued in recent times through contract problems and extended periods of lack of fights.
Earlier forecast as the next star of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a last chance - under fresh management.
He opened tentatively, with the two boxers prepared to overcommit in a calculated initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in 2022 after breaking his hand mid-fight, was competing in only his second appearance at light heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for Buatsi, who worked behind a tight guard to barely take the cleaner stanzas.
The crowd's patience wore thin because of constant clinching, with the challenger slipping to the canvas multiple occasions during clinches.
Parker finished the stronger, but multiple periods were hard to judge. However, previous titleholder Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Hatton Tribute Motivates All-Manchester Battle
In the secondary fight, Arthur defeated Rea by divided decision in a outstanding Manchester vs Manchester fight to capture the European light heavyweight title.
The venue grew hushed for a deeply poignant homage before the fight as 10 bells tolled in memory of the city's native Ricky Hatton, who passed away 46 years old in last month.
It was the premier televised fight night in the urban center since Hatton's passing. As the final chime disappeared, the stillness transitioned to a roar of "there's just one Ricky Hatton".
The action within the ring reflected the sentiment. Arthur was sent to the canvas by a left hook squarely on the chin in the second round, standing uncertainly to his position on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. From the other corner, the opponent - in rival City blue - was marked up quickly, noticeable damage developing under his eye as the pair exchanged powerful shots.
Rea, 27, connected with strong blows but the champion, thirty-four, matched the intensity with stinging uppercuts as the intensity seldom decreased over 12 rounds.
Arthur narrowly won the decision with official scores of even score, close margin and 115-112, but the two athletes were determined and full of heart, everything their hero Hatton represented.
