UK light-heavyweight Buatsi secured a victory yet underwhelming debut to life under fresh promotional backing with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a tight 10-round bout at the Manchester venue.
But Parker had his moments, delivering effective individual punches in a contest where the techniques didn't complement each other, with excessive holding disrupting the action.
The scoring judges scored it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest showing but how do champions respond? They prevail," the victor commented in the ringside as he was greeted with boos from the audience.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to claim a 20th career victory.
Various analysts felt Parker, thirty-one, deserved the victory but the British boxer suffered the second defeat of his 28-match professional journey.
Buatsi Earns Triumph in Uneventful Affair
Buatsi's progress has stalled in recent times through contract problems and extended periods of lack of fights.
Once tipped as the future of UK boxing, he now stands trying to realize his potential - possibly in what feels like a last chance - under new promotional backing.
He began cautiously, with neither fighter willing to overcommit in a calculated opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, making life awkward for the favorite, who utilized a protective stance to barely take the better periods.
The audience's tolerance diminished during regular grabbing, with the challenger falling to the floor several times during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. Although, previous titleholder Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor advances, but with the presence of heavy hitter Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Memorial Motivates Manchester Derby Fight
In the supporting bout, Lyndon Arthur beat Rea by close verdict in a outstanding Manchester vs Manchester contest to capture the European light-heavyweight championship.
The stadium became quiet for a profoundly moving tribute before the fight as 10 bells rang in honor of local hero Hatton, who succumbed 46 years old in recently.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the final chime ended, the quiet became a chant of "there's only one Hatton".
The fighting inside the ropes matched the sentiment. Arthur was sent to the canvas by a powerful punch flush on the jaw in the early round, rising shakily to his position on the referee's count.
But the Manchester United-red shorts of the fighter soon came forward again. From the other corner, Rea - in opposing blue - was damaged quickly, significant bruising appearing under his face as the pair traded hard punches.
Rea, twenty-seven, landed power punches but the champion, 34, matched the intensity with powerful upward punches as the pace hardly diminished over the full distance.
Arthur barely secured the verdict with official scores of even score, 115-113 and 115-112, but each competitor were determined and courageous, exactly what their idol the legend embodied.
