UK light heavyweight Buatsi made a winning yet disappointing start to life under fresh promotional backing with a decision win over Zach Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a tight ten-round bout at the Co-op Live Arena.
But Parker found success, connecting with powerful clean blows in a match where the styles failed to mesh, with excessive holding spoiling the action.
Two judges had it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my finest showing but what defines champions? They succeed," Buatsi stated in the ringside as he was faced disapproval from the crowd.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Several boxing experts thought Parker, thirty-one, should have been awarded the win but the contender experienced the second setback of his 28-match career.
Buatsi Earns Triumph in Slow Match
Buatsi's progress has plateaued in recent years through management issues and considerable time of inactivity.
Previously predicted as the next star of British boxing, he now finds himself trying to achieve expectations - possibly in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers ready to overcommit in a tentative opening few rounds.
Parker, whose single earlier setback 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 middle rounds, the underdog had stayed in contention, making life awkward for the favorite, who operated with a protective stance to edge the cleaner stanzas.
The crowd's patience wore thin because of regular grabbing, with the challenger falling to the floor various instances during close exchanges.
Parker ended stronger, but several stanzas were challenging to assess. Although, previous titleholder the boxing analyst - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the likes of power puncher Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Memorial Fuels All-Manchester Fight
In the supporting bout, Lyndon Arthur beat Rea by close verdict in a excellent Manchester vs Manchester fight to capture the European light heavyweight title.
The stadium grew hushed for a extremely emotional homage ahead of the contest as 10 bells tolled in honor of Manchester's own Ricky Hatton, who died aged 46 in last month.
It was the premier televised boxing event in the location since the passing of Hatton. As the concluding sound disappeared, the stillness became a roar of "there's only one Hatton".
The action during the bout reflected the sentiment. Arthur was floored by a powerful punch squarely on the jaw in the second round, rising shakily to his footing on the eight count.
But the Manchester United-red attire of Arthur soon advanced again. On the opposite side, Rea - in opposing blue - was injured soon, noticeable damage developing under his face as the duo traded hard punches.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the pace rarely dropped over the full distance.
The victor narrowly won the decision with judges scorecards of draw, close margin and clearer margin, but both fighters were determined and brave, all the qualities their hero Hatton stood for.
