UK light-heavyweight Buatsi secured a victory yet underwhelming beginning to his career under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a tight 10-round fight at the boxing arena.
But Parker had his moments, delivering effective clean blows in a match where the approaches never quite clicked, with frequent clinching disrupting the action.
The officials judged it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest display but what defines champions? They prevail," Buatsi commented in the ringside as he was faced disapproval from the spectators.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to earn a 20th pro success.
Some ringside observers felt the challenger, 31, deserved the win but the British boxer experienced the second defeat of his 28-match career.
Buatsi Claims Victory in Slow Affair
Buatsi's progress has slowed in recent times through promotional disputes and long spells of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to realize his potential - possibly in what seems like a final roll of the dice - under recent support.
He opened tentatively, with the two boxers ready to be aggressive in a tentative initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after breaking his hand during the bout, was making just his second fight at light heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who utilized a solid defense to edge the better rounds.
The crowd's patience diminished during frequent holding, with the challenger going down several times during clinches.
The underdog closed well, but many rounds were challenging to assess. However, former world champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Memorial Inspires Local Rivalry Contest
In the supporting bout, Lyndon Arthur defeated Rea by divided decision in a outstanding local rivalry battle to capture the European light heavyweight title.
The venue became quiet for a profoundly moving tribute before the fight as a bell ceremony sounded in honor of Manchester's own Ricky Hatton, who passed away at age 46 in September.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the concluding sound disappeared, the stillness transitioned to a shout of "there's just one Hatton".
The fighting within the ring equaled the sentiment. Arthur was knocked down by a powerful punch squarely on the jaw in the initial stage, rising shakily to his footing on the eight count.
But the traditional red shorts of Arthur soon came forward again. On the opposite side, Rea - in competitive blue - was marked up early, heavy swelling developing under his eye as the duo traded powerful shots.
Rea, 27, connected with strong blows but the champion, thirty-four, responded in kind with powerful upward punches as the intensity rarely dropped over twelve rounds.
Arthur edged the result with judges scorecards of 114-114, 115-113 and wider gap, but both fighters were persistent and brave, exactly what their idol the legend represented.
