UK light heavyweight Buatsi made a winning yet disappointing beginning to his career under new promoters with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a close 10-round contest at the Manchester venue.
But the challenger found success, connecting with powerful individual punches in a contest where the approaches failed to mesh, with frequent clinching spoiling the fight.
The scoring judges judged it 96-94 to Buatsi, with the third a even score.
"It wasn't my greatest showing but what do champions do? They prevail," the victor stated in the arena as he was met by boos from the audience.
The Londoner bounced back after his first professional defeat - an thrilling contest with Callum Smith in February - to claim a 20th career victory.
Several boxing experts thought the challenger, 31, deserved the win but the Derbyshire fighter endured the second loss of his 28-fight professional journey.
The Champion Secures Triumph in Dull Encounter
Buatsi's progress has slowed in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - maybe in what feels like a last chance - under fresh management.
He started carefully, with both competitors prepared to be aggressive in a tentative early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after damaging his hand during the bout, was competing in only his second bout at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a tight guard to narrowly win the better stanzas.
The crowd's patience diminished during constant clinching, with Parker falling to the floor several times during clinches.
The underdog finished the stronger, but several stanzas were difficult to score. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
The victor advances, but with the presence of hard hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Homage Fuels Local Rivalry Contest
In the co-main event, Lyndon Arthur overcame Rea by divided decision in a excellent all-Manchester contest to secure the continental championship.
The arena became quiet for a deeply poignant homage before the fight as 10 bells sounded in honor of Manchester's own Ricky Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the concluding sound faded, the silence transitioned to a shout of "only one Ricky Hatton".
The competition inside the ropes equaled the emotion. Arthur was floored by a powerful punch directly to the face in the second round, rising shakily to his position on the count of eight.
But the Manchester United-red shorts of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was damaged soon, heavy swelling developing under his eye as the pair traded punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace seldom decreased over the full distance.
Arthur edged the result with judges scorecards of draw, narrow lead and wider gap, but both fighters were relentless and courageous, everything their idol the legend stood for.
