UK light-heavyweight Buatsi earned a win yet disappointing beginning to life under new promoters with a points victory over Zach Parker in Manchester.
The Olympic medal winner's work rate likely gained him a majority decision in a competitive 10-round contest at the Manchester venue.
But Parker found success, connecting with powerful clean blows in a contest where the approaches never quite clicked, with constant grabbing marring the action.
The officials had it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my finest display but how do champions respond? They succeed," the victor said in the ringside as he was met by boos from the audience.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Various analysts thought the challenger, thirty-one, deserved the victory but the Derbyshire fighter experienced the second setback of his 28-bout career.
The Champion Secures Win in Slow Match
The fighter's advancement has slowed in the past few years through management issues and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to realize his potential - maybe in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with the two boxers prepared to take risks in a calculated initial rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in two years ago after damaging his hand in the contest, was competing in only his second fight at light-heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for the favorite, who worked behind a tight guard to edge the more effective stanzas.
The audience's tolerance wore thin because of regular grabbing, with the challenger going down various instances during close exchanges.
Parker closed well, but many rounds were challenging to assess. Nevertheless, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the caliber of heavy hitter Benavidez, and Russian champion Bivol leading the category, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Fuels All-Manchester Contest
In the supporting bout, Arthur beat Bradley Rea by close verdict in a terrific local rivalry battle to capture the continental championship.
The stadium grew hushed for a profoundly moving memorial prior to the bout as ten bells rang in honor of local hero Ricky Hatton, who succumbed aged 46 in September.
It was the first major televised match card in the location since Hatton's death. As the last bell faded, the silence gave way to a shout of "only one Hatton".
The action within the ring equaled the emotion. The eventual winner was sent to the canvas by a significant blow directly to the face in the second round, getting up unsteadily to his position on the eight count.
But the traditional red attire of the fighter soon advanced again. From the other corner, the opponent - in opposing blue - was injured early, significant bruising appearing under his orbital area as the duo exchanged powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with powerful upward punches as the action seldom decreased over the full distance.
The victor narrowly won the verdict with judges scorecards of even score, close margin and 115-112, but the two athletes were persistent and courageous, all the qualities their idol Hatton represented.
