British light heavyweight Buatsi earned a win yet underwhelming start to his career under fresh promotional backing with a decision win over Zach Parker in Manchester.
The Olympic medal winner's work rate likely gained him a majority decision in a tight 10-round bout at the boxing arena.
But the challenger found success, connecting with powerful individual punches in a match where the styles never quite clicked, with frequent clinching disrupting the contest.
The officials scored it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest display but what defines champions? They win," Buatsi commented in the ringside as he was greeted with negative reactions from the spectators.
The Londoner bounced back after his maiden career setback - an thrilling contest with Callum Smith in February - to secure a 20th career victory.
Various analysts thought Parker, 31, deserved the victory but the contender endured the second defeat of his 28-bout career.
Buatsi Claims Win in Slow Affair
The fighter's advancement has plateaued in the past few years through contract problems and long spells of lack of fights.
Previously predicted as the rising talent of the British fight scene, he now stands trying to fulfil that early promise - possibly in what feels like a last chance - under recent support.
He opened tentatively, with neither fighter ready to overcommit in a cagey initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was making just his second bout at light heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for Buatsi, who operated with a protective stance to barely take the more effective rounds.
The crowd's patience diminished during regular grabbing, with Parker falling to the floor several times during close exchanges.
Parker finished the stronger, but multiple periods were difficult to score. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Tribute Motivates Local Rivalry Contest
In the co-main event, Lyndon Arthur overcame Rea by close verdict in a outstanding local rivalry battle to secure the European light heavyweight title.
The stadium fell silent for a profoundly moving tribute before the fight as ten bells sounded in remembrance of local hero Ricky Hatton, who succumbed 46 years old in recently.
It was the premier televised fight night in the city since the passing of Hatton. As the concluding sound disappeared, the stillness gave way to a shout of "only one Ricky Hatton".
The competition within the ring equaled the sentiment. Arthur was knocked down by a powerful punch directly to the jaw in the second round, getting up unsteadily to his position on the referee's count.
But the red-colored attire of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was damaged early, noticeable damage developing under his eye as the pair landed hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with stinging uppercuts as the action hardly diminished over twelve rounds.
The victor barely secured the result with scoring tallies of even score, narrow lead and wider gap, but the two athletes were relentless and courageous, exactly what their hero the legend embodied.
