UK light-heavyweight Buatsi earned a win yet disappointing debut to life under new promoters with a points victory over Zach Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a close 10-round fight at the Manchester venue.
But Parker had his moments, connecting with powerful single shots in a fight where the techniques didn't complement each other, with frequent clinching spoiling the fight.
The scoring judges had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best showing but what do champions do? They prevail," the victor said in the arena as he was greeted with boos from the spectators.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to claim a 20th pro success.
Various analysts felt Parker, 31, deserved the victory but the contender suffered the second setback of his 28-fight professional journey.
The Champion Secures Triumph in Slow Match
The fighter's advancement has stalled in the past few years through contract problems and extended periods of lack of fights.
Once tipped as the future of British boxing, he now finds himself trying to achieve expectations - maybe in what feels like a last chance - under fresh management.
He began cautiously, with both competitors willing to overcommit in a cagey early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand during the bout, was competing in only his second fight at light-heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for the favorite, who worked behind a tight guard to narrowly win the cleaner rounds.
The crowd's patience wore thin amid frequent holding, with the challenger going down several times during grappling.
Parker closed well, but several stanzas were hard to judge. However, previous titleholder Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the presence of heavy hitter Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the co-main event, Arthur defeated Rea by divided decision in a outstanding Manchester vs Manchester contest to capture the European light heavyweight belt.
The arena grew hushed for a deeply poignant memorial prior to the bout as a bell ceremony sounded in honor of Manchester's own Hatton, who succumbed aged 46 in September.
It was the premier televised fight night in the location since the passing of Hatton. As the last bell ended, the quiet gave way to a roar of "only one Hatton".
The fighting during the bout equaled the feeling. Arthur was knocked down by a left hook directly to the chin in the early round, standing uncertainly to his position on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was injured soon, significant bruising forming under his orbital area as the pair exchanged punishing blows.
Rea, twenty-seven, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the action rarely dropped over twelve rounds.
The victor barely secured the verdict with official scores of even score, narrow lead and clearer margin, but both fighters were determined and full of heart, exactly what their inspiration the legend represented.
