British light-heavyweight Buatsi made a winning yet unimpressive beginning to his career under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a close ten-round fight at the Co-op Live Arena.
But the challenger found success, connecting with powerful clean blows in a match where the approaches didn't complement each other, with frequent clinching disrupting the contest.
Two judges judged it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my greatest performance but how do champions respond? They succeed," the victor commented in the arena as he was greeted with negative reactions from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to claim a 20th career victory.
Several boxing experts felt the challenger, 31, should have been awarded the decision but the British boxer suffered the second defeat of his 28-match career.
The Champion Earns Triumph in Slow Encounter
The fighter's advancement has slowed in recent years through contract problems and long spells of lack of fights.
Earlier forecast as the future of British boxing, he now stands trying to achieve expectations - perhaps in what feels like a final roll of the dice - under fresh management.
He began cautiously, with both competitors ready to overcommit in a calculated opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after damaging his hand mid-fight, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, Parker had kept it close, making life awkward for the favorite, who utilized a protective stance to edge the cleaner rounds.
The spectators' acceptance diminished because of constant clinching, with the challenger going down various instances during close exchanges.
The underdog finished the stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still seems difficult.
Hatton Memorial Inspires All-Manchester Battle
In the co-main event, Lyndon Arthur beat Bradley Rea by close verdict in a terrific all-Manchester fight to capture the continental championship.
The arena fell silent for a deeply poignant memorial ahead of the contest as a bell ceremony rang in honor of the city's native Hatton, who succumbed aged 46 in last month.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the final chime ended, the silence transitioned to a chant of "there's just one Hatton".
The action during the bout reflected the feeling. Arthur was knocked down by a significant blow directly to the chin in the early round, rising shakily to his position on the referee's count.
But the traditional red attire of the fighter soon advanced again. From the other corner, Rea - in opposing blue - was damaged early, heavy swelling developing under his orbital area as the duo landed powerful shots.
Rea, twenty-seven, landed power punches but the champion, 34, matched the intensity with stinging uppercuts as the pace hardly diminished over twelve rounds.
Arthur narrowly won the result with official scores of even score, 115-113 and 115-112, but both fighters were relentless and brave, exactly what their idol the legend represented.
