British light heavyweight Buatsi made a winning yet underwhelming start to his career under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a tight 10-round fight at the Manchester venue.
But Parker landed significant shots, connecting with powerful clean blows in a contest where the styles never quite clicked, with frequent clinching spoiling the fight.
Two judges scored it 96-94 to the winner, with the remaining official a even score.
"It wasn't my best performance but what do champions do? They win," the victor stated in the ring as he was faced disapproval from the crowd.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a 20th pro success.
Some ringside observers felt Parker, thirty-one, deserved the decision but the British boxer experienced the second loss of his 28-bout professional journey.
The Champion Earns Win in Uneventful Affair
Buatsi's progress has slowed in recent times through promotional disputes and long spells of lack of fights.
Earlier forecast as the next star of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a last chance - under fresh management.
He began cautiously, with neither fighter willing to take risks in a tentative early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second fight at the higher weight class.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who operated with a tight guard to barely take the cleaner periods.
The crowd's patience diminished because of regular grabbing, with the challenger falling to the floor multiple occasions during grappling.
Parker finished the stronger, but multiple periods were hard to judge. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the caliber of hard hitter Benavidez, and Russian star Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Hatton Homage Fuels All-Manchester Battle
In the secondary fight, Lyndon Arthur beat Rea by close verdict in a terrific all-Manchester fight to win the European light heavyweight championship.
The venue grew hushed for a extremely emotional tribute ahead of the contest as a bell ceremony sounded in memory of the city's native Hatton, who passed away at age 46 in last month.
It was the initial significant broadcast fight night in the location since Hatton's death. As the final chime ended, the silence gave way to a roar of "there's just one Ricky Hatton".
The competition during the bout matched the emotion. The eventual winner was sent to the canvas by a left hook flush on the chin in the initial stage, rising shakily to his footing on the eight count.
But the red-colored attire of Arthur soon came forward again. Across the ring, Rea - in rival City blue - was damaged early, noticeable damage developing under his eye as the duo traded powerful shots.
The challenger, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with effective uppercuts as the action seldom decreased over twelve rounds.
The victor edged the decision with judges scorecards of 114-114, narrow lead and clearer margin, but the two athletes were persistent and full of heart, everything their hero Hatton embodied.
