British light heavyweight Buatsi secured a victory yet disappointing beginning to life under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a close ten-round bout at the Co-op Live Arena.
But the challenger found success, connecting with powerful individual punches in a fight where the techniques failed to mesh, with frequent clinching marring the fight.
The officials scored it 96-94 to the winner, with the remaining official a even score.
"It wasn't my best performance but what do champions do? They prevail," Buatsi said in the arena as he was greeted with boos from the spectators.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to claim a 20th pro success.
Various analysts felt the challenger, thirty-one, deserved the victory but the British boxer endured the second defeat of his 28-match career.
The Champion Secures Win in Dull Affair
The fighter's advancement has plateaued in recent years through management issues and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now finds himself trying to realize his potential - maybe in what appears to be a last chance - under recent support.
He started carefully, with neither fighter willing to take risks in a tentative opening few rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in 2022 after suffering a hand injury during the bout, was making just his second fight at light heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for Buatsi, who worked behind a tight guard to edge the cleaner periods.
The crowd's patience diminished because of constant clinching, with Parker falling to the floor multiple occasions during close exchanges.
The underdog closed well, but several stanzas were difficult to score. However, former world champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just one round.
Buatsi progresses, but with the caliber of heavy hitter Benavidez, and Russian star Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Fuels Local Rivalry Battle
In the supporting bout, Lyndon Arthur overcame Rea by close verdict in a terrific local rivalry contest to capture the European light heavyweight championship.
The venue grew hushed for a deeply poignant homage before the fight as ten bells tolled in memory of Manchester's own Ricky Hatton, who succumbed at age 46 in September.
It was the first major televised fight night in the location since Hatton's passing. As the last bell faded, the silence gave way to a shout of "there's just one Ricky Hatton".
The competition within the ring matched the emotion. The eventual winner was knocked down by a powerful punch directly to the chin in the second round, rising shakily to his position on the eight count.
But the traditional red attire of Arthur soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was marked up quickly, noticeable damage forming under his face as the pair traded punishing blows.
Rea, 27, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the pace hardly diminished over twelve rounds.
Arthur edged the decision with judges scorecards of 114-114, narrow lead and wider gap, but each competitor were determined and courageous, exactly what their idol the legend represented.
