British light heavyweight Buatsi made a winning yet underwhelming start to life under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a tight ten-round fight at the boxing arena.
But Parker landed significant shots, delivering effective clean blows in a match where the styles never quite clicked, with excessive holding disrupting the fight.
The officials scored it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my finest showing but what do champions do? They win," Buatsi said in the ringside as he was greeted with disapproval from the crowd.
The Londoner bounced back after his initial pro loss - an epic battle with his previous opponent in February - to earn a 20th pro success.
Some ringside observers felt the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter suffered the second setback of his 28-bout professional journey.
Buatsi Claims Win in Slow Affair
The fighter's advancement has slowed in recent years through contract problems and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to realize his potential - possibly in what feels like a final roll of the dice - under recent support.
He started carefully, with the two boxers ready to overcommit in a cagey opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to barely take the more effective periods.
The audience's tolerance wore thin during frequent holding, with Parker falling to the floor multiple occasions during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. However, previous titleholder Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
Buatsi advances, but with the likes of hard hitter Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Memorial Fuels Local Rivalry Contest
In the co-main event, Lyndon Arthur defeated Rea by split-decision in a excellent local rivalry contest to secure the continental belt.
The venue fell silent for a deeply poignant homage ahead of the contest as ten bells sounded in remembrance of Manchester's own Ricky Hatton, who succumbed at age 46 in recently.
It was the first major televised boxing event in the city since Hatton's passing. As the concluding sound faded, the quiet transitioned to a shout of "only one Hatton".
The fighting during the bout reflected the emotion. The eventual winner was knocked down by a significant blow flush on the face in the early round, rising shakily to his feet on the eight count.
But the Manchester United-red shorts of Arthur soon came forward again. On the opposite side, Rea - in competitive blue - was damaged soon, heavy swelling developing under his face as the fighters traded hard punches.
Rea, 27, connected with strong blows but the champion, 34, responded in kind with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor edged the verdict with judges scorecards of draw, close margin and wider gap, but both fighters were persistent and courageous, exactly what their hero Hatton stood for.
