British light-heavyweight Buatsi secured a victory yet disappointing start to life under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a close ten-round fight at the boxing arena.
But the challenger had his moments, connecting with powerful clean blows in a contest where the styles failed to mesh, with constant grabbing marring the action.
The scoring judges scored it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best display but what do champions do? They prevail," the victor stated in the arena as he was met by disapproval from the audience.
The British fighter bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts felt Parker, 31, should have been awarded the win but the British boxer suffered the second defeat of his 28-match career.
Buatsi Secures Win in Uneventful Match
The fighter's advancement has stalled in the past few years through management issues and long spells of lack of fights.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with neither fighter ready to take risks in a cagey opening few rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the fight's midpoint, Parker had made it competitive, creating difficulties for the favorite, who worked behind a solid defense to edge the better periods.
The audience's tolerance wore thin because of constant clinching, with the challenger falling to the floor various instances during grappling.
Parker closed well, but many rounds were challenging to assess. Nevertheless, ex-champion Carl Frampton - commentating on Dazn - had it particularly wide for Parker, awarding Buatsi just a single round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Contest
In the secondary fight, Lyndon Arthur overcame Rea by divided decision in a terrific all-Manchester contest to win the continental belt.
The stadium became quiet for a extremely emotional homage before the fight as a bell ceremony rang in memory of Manchester's own Hatton, who succumbed 46 years old in September.
It was the premier televised match card in the city since Hatton's death. As the final chime faded, the stillness gave way to a roar of "only one Ricky Hatton".
The fighting within the ring matched the sentiment. The eventual winner was floored by a powerful punch flush on the jaw in the initial stage, rising shakily to his feet on the eight count.
But the red-colored attire of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was damaged early, noticeable damage forming under his face as the fighters landed hard punches.
The challenger, 27, landed power punches but the champion, 34, responded in kind with stinging uppercuts as the action rarely dropped over the full distance.
The victor edged the verdict with judges scorecards of 114-114, 115-113 and clearer margin, but both fighters were persistent and courageous, exactly what their idol the legend represented.
