UK light heavyweight Buatsi secured a victory yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a split decision in a tight ten-round bout at the Manchester venue.
But the challenger found success, connecting with powerful clean blows in a fight where the approaches never quite clicked, with excessive holding marring the fight.
Two judges judged it 96-94 for to Buatsi, with the third a even score.
"It wasn't my finest display but how do champions respond? They win," the victor commented in the ring as he was greeted with negative reactions from the crowd.
The British fighter got back to winning after his first professional defeat - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers felt Parker, thirty-one, should have been awarded the win but the contender endured the second setback of his 28-fight career.
The Champion Earns Win in Dull Encounter
The fighter's advancement has slowed in the past few years through management issues and extended periods of inactivity.
Once tipped as the next star of British boxing, he now stands trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, with neither fighter ready to be aggressive in a tentative initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after damaging his hand in the contest, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who worked behind a protective stance to narrowly win the cleaner stanzas.
The spectators' acceptance decreased amid constant clinching, with the challenger going down several times during grappling.
Parker closed well, but multiple periods were hard to judge. However, previous titleholder Carl Frampton - working with the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the caliber of power puncher Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Hatton Tribute Inspires All-Manchester Battle
In the supporting bout, Arthur overcame Rea by split-decision in a outstanding Manchester vs Manchester contest to capture the European light heavyweight belt.
The stadium fell silent for a deeply poignant homage before the fight as a bell ceremony tolled in remembrance of local hero Ricky Hatton, who passed away at age 46 in last month.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the concluding sound faded, the quiet gave way to a shout of "there's just one Ricky Hatton".
The fighting within the ring reflected the sentiment. The eventual winner was knocked down by a left hook squarely on the chin in the initial stage, standing uncertainly to his feet on the count of eight.
But the red-colored equipment of the fighter soon came forward again. On the opposite side, Rea - in opposing blue - was marked up quickly, noticeable damage appearing under his orbital area as the pair exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the intensity rarely dropped over twelve rounds.
Arthur barely secured the verdict with official scores of draw, narrow lead and 115-112, but each competitor were persistent and full of heart, exactly what their inspiration Hatton stood for.
