UK light heavyweight Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a close 10-round contest at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a match where the approaches never quite clicked, with frequent clinching marring the action.
The officials had it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my finest performance but how do champions respond? They win," Buatsi stated in the arena as he was greeted with boos from the audience.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to secure a twentieth professional win.
Various analysts believed the challenger, thirty-one, merited the win but the British boxer endured the second setback of his 28-match professional journey.
Buatsi Earns Victory in Dull Encounter
His career development has slowed in recent years through promotional disputes and long spells of inactivity.
Earlier forecast as the future of British boxing, he now stands trying to achieve expectations - perhaps in what feels like a last chance - under recent support.
He began cautiously, with the two boxers prepared to be aggressive in a cagey early stages.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, causing problems for the favorite, who worked behind a solid defense to narrowly win the better rounds.
The crowd's patience diminished during frequent holding, with Parker falling to the floor multiple occasions during grappling.
Parker finished the stronger, but many rounds were difficult to score. However, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the presence of hard hitter Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels All-Manchester Contest
In the secondary fight, Lyndon Arthur beat Rea by divided decision in a outstanding all-Manchester battle to capture the European light-heavyweight title.
The arena grew hushed for a profoundly moving homage ahead of the contest as 10 bells rang in honor of local hero Ricky Hatton, who succumbed at age 46 in September.
It was the premier televised fight night in the urban center since the passing of Hatton. As the concluding sound disappeared, the quiet became a shout of "there's just one Hatton".
The action inside the ropes equaled the sentiment. Arthur was floored by a powerful punch directly to the chin in the second round, standing uncertainly to his position on the count of eight.
But the traditional red attire of Arthur soon pressed ahead again. From the other corner, Rea - in rival City blue - was injured early, noticeable damage forming under his face as the pair landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with powerful upward punches as the pace seldom decreased over 12 rounds.
Arthur barely secured the decision with scoring tallies of draw, close margin and wider gap, but the two athletes were relentless and courageous, all the qualities their inspiration Hatton embodied.
