British light heavyweight Buatsi earned a win yet underwhelming start to life under fresh promotional backing with a decision win over Zach Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a competitive 10-round bout at the Co-op Live Arena.
But Parker found success, landing some telling single shots in a match where the styles didn't complement each other, with frequent clinching marring the action.
The officials had it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my best display but what do champions do? They prevail," the victor said in the arena as he was met by negative reactions from the audience.
The Londoner bounced back after his initial pro loss - an epic battle with Callum Smith in February - to secure a 20th pro success.
Various analysts thought Parker, 31, should have been awarded the victory but the British boxer endured the second defeat of his 28-bout professional journey.
Buatsi Earns Victory in Uneventful Encounter
The fighter's advancement has stalled in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the next star of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter ready to take risks in a calculated early stages.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was participating in his second appearance at light heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for Buatsi, who worked behind a tight guard to barely take the more effective rounds.
The audience's tolerance decreased during regular grabbing, with the challenger slipping to the canvas several times during close exchanges.
Parker ended stronger, but several stanzas were hard to judge. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Hatton Tribute Motivates All-Manchester Contest
In the co-main event, Arthur defeated Bradley Rea by divided decision in a terrific local rivalry battle to secure the continental belt.
The arena fell silent for a deeply poignant memorial before the fight as a bell ceremony tolled in remembrance of the city's native Ricky Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast fight night in the urban center since Hatton's passing. As the last bell ended, the stillness transitioned to a roar of "there's only one Hatton".
The competition within the ring matched the emotion. The eventual winner was sent to the canvas by a left hook flush on the jaw in the second round, getting up unsteadily to his position on the count of eight.
But the Manchester United-red attire of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was marked up quickly, heavy swelling forming under his face as the pair traded powerful shots.
Rea, 27, landed power punches but Arthur, 34, responded in kind with powerful upward punches as the intensity seldom decreased over twelve rounds.
Arthur barely secured the verdict with judges scorecards of even score, 115-113 and 115-112, but each competitor were relentless and full of heart, exactly what their hero the legend represented.
