British light heavyweight Buatsi earned a win yet unimpressive beginning to his career under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a majority 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 approaches failed to mesh, with constant grabbing marring the fight.
The officials judged it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my greatest performance but how do champions respond? They prevail," Buatsi stated in the ringside as he was faced boos from the audience.
The British fighter bounced back after his initial pro loss - an thrilling contest with Callum Smith in February - to secure a 20th pro success.
Several boxing experts believed the challenger, 31, should have been awarded the decision but the contender experienced the second defeat of his 28-fight professional journey.
The Champion Claims Triumph in Slow Encounter
Buatsi's progress has slowed in recent times through promotional disputes and extended periods of lack of fights.
Once tipped as the next star of UK boxing, he now stands trying to fulfil that early promise - maybe in what feels like a last chance - under new promotional backing.
He started carefully, with both competitors willing to be aggressive in a calculated initial rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was competing in only his second appearance at light heavyweight.
By the halfway stage, Parker had stayed in contention, creating difficulties for the favorite, who operated with a solid defense to narrowly win the cleaner stanzas.
The crowd's patience diminished during regular grabbing, with the challenger slipping to the canvas several times during clinches.
The underdog closed well, but several stanzas were challenging to assess. Although, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just one round.
The victor advances, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Motivates Manchester Derby Contest
In the secondary fight, Lyndon Arthur beat Rea by close verdict in a terrific all-Manchester contest to capture the European light heavyweight belt.
The venue grew hushed for a profoundly moving memorial prior to the bout as a bell ceremony tolled in memory of local hero Ricky Hatton, who succumbed 46 years old in recently.
It was the first major televised boxing event in the city since the passing of Hatton. As the concluding sound disappeared, the quiet became a roar of "there's only one Hatton".
The competition inside the ropes matched the sentiment. The eventual winner was floored by a powerful punch squarely on the face in the early round, getting up unsteadily to his position on the count of eight.
But the Manchester United-red equipment of Arthur soon came forward again. From the other corner, the opponent - in opposing blue - was injured early, significant bruising appearing under his eye as the pair exchanged powerful shots.
Rea, 27, connected with strong blows but the champion, 34, fought fire with fire with powerful upward punches as the pace hardly diminished over the full distance.
Arthur barely secured the result with scoring tallies of 114-114, narrow lead and 115-112, but the two athletes were relentless and full of heart, exactly what their hero Hatton represented.
