British light-heavyweight Buatsi earned a win yet disappointing beginning to his career under recent management with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a close ten-round fight at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful clean blows in a contest where the styles never quite clicked, with constant grabbing disrupting the fight.
Two judges judged it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my greatest display but what do champions do? They succeed," Buatsi said in the ringside as he was greeted with boos from the spectators.
The Londoner got back to winning after his first professional defeat - an epic battle with Callum Smith in February - to earn a twentieth professional win.
Various analysts believed the challenger, 31, should have been awarded the win but the British boxer experienced the second loss of his 28-fight professional journey.
The Champion Earns Win in Slow Affair
Buatsi's progress has stalled in recent times through contract problems and extended periods of inactivity.
Previously predicted as the next star of British boxing, he now stands trying to achieve expectations - possibly in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter willing to take risks in a tentative opening few rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after damaging his hand during the bout, was making just his second fight at the higher weight class.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who operated with a solid defense to narrowly win the better stanzas.
The spectators' acceptance wore thin amid constant clinching, with Parker falling to the floor several times during grappling.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, previous titleholder Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Tribute Motivates Local Rivalry Contest
In the co-main event, Arthur defeated Bradley Rea by split-decision in a terrific Manchester vs Manchester contest to secure the European light-heavyweight belt.
The arena fell silent for a deeply poignant homage prior to the bout as 10 bells rang in memory of Manchester's own Ricky Hatton, who passed away at age 46 in last month.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the concluding sound ended, the quiet became a shout of "there's only one Hatton".
The competition inside the ropes equaled the emotion. The eventual winner was floored by a powerful punch directly to the jaw in the initial stage, getting up unsteadily to his position on the count of eight.
But the traditional red equipment of Arthur soon came forward again. Across the ring, Rea - in competitive blue - was marked up soon, heavy swelling appearing under his eye as the fighters landed punishing blows.
Rea, twenty-seven, landed power punches but the champion, 34, matched the intensity with effective uppercuts as the intensity seldom decreased over twelve rounds.
Arthur edged the decision with scoring tallies of draw, 115-113 and clearer margin, but each competitor were persistent and courageous, exactly what their inspiration the legend stood for.
