UK light heavyweight Buatsi secured a victory yet underwhelming beginning to life under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a split decision in a competitive 10-round fight at the boxing arena.
But the challenger landed significant shots, delivering effective single shots in a match where the styles didn't complement each other, with excessive holding spoiling the fight.
The officials had it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my finest showing but what defines champions? They prevail," Buatsi commented in the ringside as he was faced boos from the audience.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Various analysts thought the challenger, 31, deserved the victory but the British boxer endured the second setback of his 28-match career.
The Champion Earns Triumph in Slow Encounter
The fighter's advancement has stalled in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under recent support.
He started carefully, with both competitors ready to overcommit in a cagey opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after damaging his hand mid-fight, was participating in his second bout at light-heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who utilized a solid defense to narrowly win the cleaner rounds.
The crowd's patience diminished during regular grabbing, with Parker going down several times during close exchanges.
The underdog ended stronger, but several stanzas were challenging to assess. Nevertheless, ex-champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - based on this performance - still looks steep.
Hatton Tribute Fuels Local Rivalry Battle
In the supporting bout, Lyndon Arthur overcame Rea by close verdict in a outstanding local rivalry fight to win the continental belt.
The stadium became quiet for a profoundly moving homage prior to the bout as ten bells rang in remembrance of the city's native Ricky Hatton, who succumbed 46 years old in September.
It was the premier televised fight night in the location since Hatton's passing. As the final chime disappeared, the silence became a shout of "there's just one Ricky Hatton".
The action within the ring equaled the emotion. The eventual winner was floored by a left hook squarely on the jaw in the second round, standing uncertainly to his position on the referee's count.
But the traditional red attire of Arthur soon pressed ahead again. Across the ring, the opponent - in opposing blue - was marked up quickly, significant bruising appearing under his face as the pair landed hard punches.
Rea, 27, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the intensity hardly diminished over 12 rounds.
The victor barely secured the decision with judges scorecards of even score, close margin and 115-112, but each competitor were determined and courageous, everything their hero the legend embodied.
