UK light heavyweight Buatsi secured a victory yet disappointing start to life under recent management with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a close 10-round bout at the boxing arena.
But Parker had his moments, landing some telling single shots in a fight where the styles failed to mesh, with frequent clinching spoiling the action.
The officials scored it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my best performance but what do champions do? They win," the victor commented in the ring as he was faced disapproval from the crowd.
The Londoner bounced back after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a 20th career victory.
Several boxing experts believed the challenger, 31, merited the win but the Derbyshire fighter experienced the second loss of his 28-match professional journey.
Buatsi Claims Triumph in Slow Affair
His career development has plateaued in the past few years through contract problems and extended periods of inactivity.
Earlier forecast as the next star of UK boxing, he now is positioned trying to realize his potential - possibly in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with the two boxers willing to overcommit in a cagey early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, causing problems for the favorite, who worked behind a tight guard to barely take the better stanzas.
The crowd's patience decreased because of constant clinching, with Parker falling to the floor various instances during grappling.
The underdog closed well, but many rounds were difficult to score. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, awarding Buatsi just one round.
The victor progresses, but with the caliber of hard hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Hatton Tribute Motivates All-Manchester Fight
In the secondary fight, Arthur overcame Bradley Rea by split-decision in a outstanding local rivalry battle to secure the continental belt.
The stadium grew hushed for a deeply poignant tribute before the fight as 10 bells tolled in honor of local hero Ricky Hatton, who died at age 46 in recently.
It was the first major televised fight night in the city since the passing of Hatton. As the last bell faded, the stillness transitioned to a roar of "only one Ricky Hatton".
The fighting inside the ropes equaled the sentiment. Arthur was sent to the canvas by a powerful punch directly to the jaw in the early round, getting up unsteadily to his footing on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in opposing blue - was injured quickly, significant bruising appearing under his eye as the duo exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with powerful upward punches as the intensity seldom decreased over 12 rounds.
Arthur edged the decision with official scores of even score, close margin and 115-112, but each competitor were relentless and courageous, all the qualities their hero Hatton stood for.
