British light heavyweight Buatsi secured a victory yet disappointing debut to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a split decision in a close ten-round bout at the Manchester venue.
But the challenger found success, landing some telling clean blows in a fight where the approaches didn't complement each other, with excessive holding marring the action.
Two judges scored it 96-94 for to the winner, with the final judge a even score.
"It wasn't my finest showing but what defines champions? They win," the victor stated in the ringside as he was faced disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Various analysts thought the challenger, 31, should have been awarded the victory but the contender suffered the second setback of his 28-fight professional journey.
The Champion Claims Triumph in Slow Encounter
His career development has plateaued in recent years through promotional disputes and long spells of lack of fights.
Previously predicted as the next star of British boxing, he now is positioned trying to achieve expectations - possibly in what feels like a last chance - under fresh management.
He started carefully, with the two boxers willing to overcommit in a calculated initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand mid-fight, was competing in only his second fight at light heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for the favorite, who utilized a solid defense to edge the more effective periods.
The audience's tolerance wore thin because of constant clinching, with the challenger falling to the floor various instances during clinches.
Parker ended stronger, but many rounds were difficult to score. Although, previous titleholder Carl Frampton - commentating on Dazn - had it particularly wide for Parker, giving Buatsi just a single round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Hatton Tribute Inspires Manchester Derby Contest
In the secondary fight, Lyndon Arthur overcame Rea by split-decision in a excellent all-Manchester fight to capture the European light-heavyweight title.
The arena fell silent for a profoundly moving memorial before the fight as a bell ceremony rang in memory of the city's native Ricky Hatton, who succumbed aged 46 in last month.
It was the first major televised fight night in the urban center since Hatton's passing. As the last bell disappeared, the quiet became a chant of "there's only one Ricky Hatton".
The action during the bout equaled the sentiment. The eventual winner was floored by a significant blow squarely on the face in the second round, getting up unsteadily to his footing on the eight count.
But the Manchester United-red attire of Arthur soon came forward again. Across the ring, Rea - in rival City blue - was injured quickly, heavy swelling developing under his orbital area as the duo landed hard punches.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the action seldom decreased over twelve rounds.
The victor narrowly won the result with judges scorecards of 114-114, 115-113 and 115-112, but the two athletes were determined and courageous, everything their hero Hatton stood for.
