UK light-heavyweight Buatsi made a winning yet underwhelming beginning to his career under fresh promotional backing with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a tight ten-round fight at the Manchester venue.
But the challenger found success, landing some telling individual punches in a fight where the techniques didn't complement each other, with excessive holding marring the contest.
Two judges judged it 96-94 for to the winner, with the third a even score.
"It wasn't my best performance but what defines champions? They succeed," Buatsi stated in the ring as he was met by boos from the spectators.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to claim a 20th pro success.
Several boxing experts thought the challenger, 31, merited the decision but the British boxer endured the second defeat of his 28-match career.
Buatsi Claims Victory in Slow Match
His career development has stalled in the past few years through contract problems and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to achieve expectations - perhaps in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers prepared to take risks in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was participating in his second fight at the higher weight class.
By the middle rounds, the underdog had made it competitive, creating difficulties for the favorite, who utilized a tight guard to barely take the more effective periods.
The crowd's patience diminished during frequent holding, with Parker slipping to the canvas various instances during grappling.
Parker finished the stronger, but multiple periods were difficult to score. However, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Homage Motivates Manchester Derby Contest
In the secondary fight, Arthur overcame Rea by divided decision in a outstanding local rivalry fight to capture the continental title.
The stadium grew hushed for a profoundly moving homage prior to the bout as a bell ceremony sounded in memory of Manchester's own Hatton, who died at age 46 in last month.
It was the premier televised fight night in the location since Hatton's passing. As the concluding sound disappeared, the silence became a shout of "only one Ricky Hatton".
The competition inside the ropes reflected the emotion. Arthur was sent to the canvas by a left hook squarely on the chin in the early round, getting up unsteadily to his feet on the referee's count.
But the red-colored equipment of the fighter soon pressed ahead again. From the other corner, Rea - in competitive blue - was marked up soon, noticeable damage forming under his eye as the fighters exchanged powerful shots.
Rea, twenty-seven, landed power punches but Arthur, 34, matched the intensity with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur edged the verdict with judges scorecards of 114-114, 115-113 and 115-112, but the two athletes were determined and brave, exactly what their inspiration Hatton represented.
