UK light heavyweight Buatsi secured a victory yet unimpressive beginning to his career under recent management with a decision win over Zach Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a tight ten-round fight at the Manchester venue.
But Parker had his moments, landing some telling single shots in a match where the styles failed to mesh, with frequent clinching spoiling the fight.
Two judges had it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my best display but what do champions do? They win," the victor said in the ringside as he was faced negative reactions from the audience.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Some ringside observers felt the challenger, 31, deserved the win but the British boxer endured the second setback of his 28-match professional journey.
The Champion Claims Win in Slow Match
Buatsi's progress has stalled in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the future of British boxing, he now stands trying to fulfil that early promise - perhaps in what appears to be a last chance - under recent support.
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 his former opponent in two years ago after damaging his hand in the contest, was participating in his second bout at light-heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for the favorite, who operated with a tight guard to edge the cleaner rounds.
The spectators' acceptance decreased during regular grabbing, with the challenger going down multiple occasions during grappling.
The underdog ended stronger, but several stanzas were difficult to score. Nevertheless, previous titleholder Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just a single round.
The victor advances, but with the caliber of power puncher Benavidez, and Russian champion Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Homage Inspires Local Rivalry Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific Manchester vs Manchester contest to capture the continental belt.
The arena grew hushed for a deeply poignant memorial prior to the bout as ten bells sounded in honor of local hero Ricky Hatton, who succumbed aged 46 in recently.
It was the premier televised match card in the location since the passing of Hatton. As the concluding sound ended, the quiet became a chant of "there's only one Hatton".
The fighting inside the ropes reflected the emotion. Arthur was floored by a left hook flush on the face in the initial stage, rising shakily to his position on the count of eight.
But the traditional red attire of Arthur soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was marked up soon, noticeable damage developing under his eye as the fighters traded punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, 34, fought fire with fire with stinging uppercuts as the pace hardly diminished over twelve rounds.
The victor barely secured the decision with judges scorecards of even score, 115-113 and wider gap, but the two athletes were relentless and full of heart, exactly what their inspiration Hatton stood for.
