UK light heavyweight Buatsi earned a win yet disappointing start to life under new promoters with a decision win over Zach Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive 10-round contest at the Co-op Live Arena.
But Parker found success, connecting with powerful clean blows in a match where the techniques failed to mesh, with constant grabbing marring the fight.
The officials judged it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my finest performance but what do champions do? They prevail," the victor commented in the ringside as he was greeted with boos from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Several boxing experts felt Parker, thirty-one, deserved the win but the contender endured the second loss of his 28-bout professional journey.
The Champion Secures Victory in Dull Match
The fighter's advancement has slowed in recent years through management issues and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to achieve expectations - possibly in what feels like a ultimate opportunity - under fresh management.
He opened tentatively, with neither fighter willing to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was competing in only his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for the favorite, who utilized a tight guard to narrowly win the more effective stanzas.
The crowd's patience wore thin during constant clinching, with Parker going down various instances during close exchanges.
Parker ended stronger, but multiple periods were challenging to assess. Although, previous titleholder the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just a single round.
Buatsi advances, but with the caliber of hard hitter Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates Local Rivalry Contest
In the secondary fight, Lyndon Arthur beat Rea by close verdict in a terrific Manchester vs Manchester battle to win the European light heavyweight belt.
The stadium became quiet for a profoundly moving tribute before the fight as ten bells tolled in memory of the city's native Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast match card in the city since Hatton's death. As the last bell disappeared, the quiet transitioned to a roar of "only one Ricky Hatton".
The competition during the bout equaled the sentiment. Arthur was floored by a powerful punch flush on the face in the second round, rising shakily to his feet on the eight count.
But the Manchester United-red attire of Arthur soon came forward again. Across the ring, Rea - in opposing blue - was marked up quickly, heavy swelling appearing under his eye as the duo exchanged powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, responded in kind with effective uppercuts as the intensity rarely dropped over the full distance.
The victor edged the verdict with judges scorecards of even score, 115-113 and clearer margin, but the two athletes were persistent and brave, everything their hero Hatton embodied.
