UK light heavyweight Buatsi made a winning yet unimpressive start to his career under recent management with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But Parker landed significant shots, delivering effective clean blows in a contest where the approaches never quite clicked, with constant grabbing marring the contest.
Two judges scored it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my best showing but what do champions do? They prevail," the victor said in the ring as he was greeted with negative reactions from the audience.
The British fighter bounced back after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts felt Parker, thirty-one, should have been awarded the win but the Derbyshire fighter suffered the second setback of his 28-bout professional journey.
The Champion Earns Win in Slow Affair
The fighter's advancement has slowed in the past few years through contract problems and considerable time of inactivity.
Previously predicted as the next star of British boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a last chance - under recent support.
He started carefully, with neither fighter willing to take risks in a tentative early stages.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second bout at the higher weight class.
By the middle rounds, Parker had kept it close, causing problems for Buatsi, who operated with a protective stance to barely take the more effective stanzas.
The crowd's patience decreased amid frequent holding, with Parker going down multiple occasions during grappling.
The underdog finished the stronger, but many rounds were hard to judge. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi progresses, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Inspires Manchester Derby Battle
In the secondary fight, Arthur overcame Bradley Rea by divided decision in a terrific all-Manchester contest to secure the European light heavyweight belt.
The venue fell silent for a deeply poignant homage ahead of the contest as 10 bells tolled in memory of Manchester's own Hatton, who passed away 46 years old in last month.
It was the premier televised match card in the city since the passing of Hatton. As the concluding sound disappeared, the stillness gave way to a chant of "only one Ricky Hatton".
The action within the ring matched the feeling. The eventual winner was sent to the canvas by a left hook squarely on the chin in the early round, standing uncertainly to his position on the eight count.
But the traditional red equipment of Arthur soon advanced again. From the other corner, the opponent - in opposing blue - was damaged quickly, heavy swelling forming under his orbital area as the pair landed punishing blows.
Rea, 27, connected with strong blows but Arthur, 34, matched the intensity with effective uppercuts as the intensity rarely dropped over the full distance.
Arthur edged the decision with official scores of 114-114, narrow lead and clearer margin, but the two athletes were relentless and courageous, exactly what their idol the legend stood for.
