UK light-heavyweight Buatsi made a winning yet disappointing debut to his career under fresh promotional backing with a decision win over Zach Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a competitive 10-round contest at the Co-op Live Arena.
But Parker found success, delivering effective single shots in a match where the styles didn't complement each other, with constant grabbing spoiling the action.
Two judges had it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my best performance but how do champions respond? They prevail," Buatsi stated in the ringside as he was met by negative reactions from the crowd.
The Londoner got back to winning after his first professional defeat - an epic battle with Callum Smith in last winter - to earn a twentieth professional win.
Various analysts believed the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter suffered the second defeat of his 28-match professional journey.
The Champion Claims Victory in Slow Match
The fighter's advancement has stalled in recent times through promotional disputes and extended periods of inactivity.
Once tipped as the rising talent of UK boxing, he now is positioned trying to realize his potential - possibly in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with neither fighter prepared to be aggressive in a tentative opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was making just his second appearance at light-heavyweight.
By the middle rounds, Parker had made it competitive, causing problems for Buatsi, who utilized a tight guard to narrowly win the cleaner stanzas.
The spectators' acceptance diminished because of frequent holding, with Parker falling to the floor several times during close exchanges.
Parker ended stronger, but several stanzas were hard to judge. Although, previous titleholder the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the caliber of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Hatton Tribute Inspires All-Manchester Battle
In the secondary fight, Lyndon Arthur overcame Rea by divided decision in a outstanding local rivalry contest to capture the continental championship.
The stadium fell silent for a extremely emotional memorial prior to the bout as 10 bells sounded in memory of local hero Ricky Hatton, who passed away aged 46 in September.
It was the premier televised match card in the location since Hatton's passing. As the final chime disappeared, the stillness became a roar of "there's only one Hatton".
The competition inside the ropes matched the sentiment. The eventual winner was floored by a left hook directly to the face in the early round, getting up unsteadily to his position on the eight count.
But the traditional red equipment of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was injured quickly, heavy swelling forming under his orbital area as the pair exchanged hard punches.
Rea, 27, connected with strong blows but the champion, 34, fought fire with fire with stinging uppercuts as the pace hardly diminished over twelve rounds.
The victor edged the verdict with official scores of even score, narrow lead and 115-112, but the two athletes were persistent and brave, exactly what their idol the legend represented.
