UK light-heavyweight Buatsi made a winning yet unimpressive beginning to his career under new promoters with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a close ten-round bout at the Manchester venue.
But Parker found success, delivering effective single shots in a match where the techniques didn't complement each other, with frequent clinching spoiling the action.
The officials had it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They win," Buatsi commented in the ring as he was faced boos from the crowd.
The British fighter bounced back after his initial pro loss - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers thought Parker, 31, should have been awarded the victory but the British boxer endured the second defeat of his 28-bout professional journey.
The fighter's advancement has stalled in the past few years through promotional disputes and considerable time of lack of fights.
Earlier forecast as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a last chance - under fresh management.
He began cautiously, with both competitors ready to take risks in a cagey opening few rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a solid defense to narrowly win the cleaner periods.
The crowd's patience decreased because of constant clinching, with Parker going down various instances during clinches.
The underdog finished the stronger, but multiple periods were challenging to assess. However, previous titleholder Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
The victor moves on, but with the presence of power puncher Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a excellent all-Manchester battle to capture the European light heavyweight title.
The arena grew hushed for a extremely emotional tribute before the fight as 10 bells sounded in remembrance of the city's native Ricky Hatton, who passed away at age 46 in last month.
It was the first major televised match card in the city since Hatton's passing. As the final chime ended, the silence became a shout of "there's only one Ricky Hatton".
The action during the bout matched the feeling. The eventual winner was sent to the canvas by a significant blow flush on the face in the initial stage, rising shakily to his feet on the referee's count.
But the red-colored equipment of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was injured early, significant bruising appearing under his face as the fighters traded hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with powerful upward punches as the pace rarely dropped over the full distance.
Arthur barely secured the result with official scores of 114-114, 115-113 and 115-112, but both fighters were determined and brave, everything their idol Hatton represented.
A seasoned business consultant with over 15 years of experience in urban development and startup ecosystems across Europe.