UK light heavyweight Buatsi earned a win yet underwhelming beginning to life under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a close ten-round contest at the Manchester venue.
But Parker found success, delivering effective individual punches in a contest where the approaches failed to mesh, with frequent clinching spoiling the contest.
The scoring judges had it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest display but what do champions do? They prevail," Buatsi commented in the ring as he was faced negative reactions from the crowd.
The Londoner bounced back after his initial pro loss - an epic battle with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers thought the challenger, thirty-one, should have been awarded the decision but the British boxer experienced the second setback of his 28-match career.
Buatsi Secures Victory in Dull Match
Buatsi's progress has stalled in the past few years through contract problems and extended periods of inactivity.
Earlier forecast as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a last chance - under fresh management.
He began cautiously, with both competitors willing to overcommit in a calculated initial rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in 2022 after suffering a hand injury mid-fight, was participating in his second fight at light-heavyweight.
By the middle rounds, the underdog had kept it close, causing problems for the favorite, who operated with a solid defense to barely take the better periods.
The crowd's patience diminished because of constant clinching, with Parker slipping to the canvas multiple occasions during close exchanges.
Parker finished the stronger, but many rounds were challenging to assess. Nevertheless, ex-champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor advances, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Inspires All-Manchester Battle
In the supporting bout, Lyndon Arthur overcame Rea by split-decision in a terrific Manchester vs Manchester battle to win the continental belt.
The arena grew hushed for a deeply poignant memorial prior to the bout as ten bells tolled in remembrance of the city's native Hatton, who succumbed at age 46 in September.
It was the premier televised match card in the city since Hatton's passing. As the final chime disappeared, the silence gave way to a shout of "only one Ricky Hatton".
The competition within the ring matched the feeling. The eventual winner was sent to the canvas by a left hook directly to the jaw in the second round, standing uncertainly to his footing on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. From the other corner, Rea - in rival City blue - was injured soon, heavy swelling appearing under his eye as the duo exchanged hard punches.
Rea, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with powerful upward punches as the action seldom decreased over twelve rounds.
The victor narrowly won the verdict with judges scorecards of draw, narrow lead and clearer margin, but the two athletes were relentless and brave, exactly what their idol the legend stood for.
