British light heavyweight Buatsi made a winning yet unimpressive start to his career under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a competitive ten-round contest at the Manchester venue.
But the challenger found success, delivering effective individual punches in a contest where the techniques never quite clicked, with frequent clinching marring the fight.
The officials had it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my best display but what defines champions? They succeed," the victor commented in the ringside as he was faced disapproval from the spectators.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to earn a 20th career victory.
Various analysts thought the challenger, 31, merited the decision but the Derbyshire fighter suffered the second setback of his 28-fight professional journey.
Buatsi Claims Triumph in Slow Affair
The fighter's advancement has stalled in the past few years through management issues and considerable time of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what appears to be a last chance - under fresh management.
He began cautiously, with the two boxers ready to overcommit in a tentative initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was participating in his second fight at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for the favorite, who worked behind a tight guard to barely take the cleaner stanzas.
The audience's tolerance decreased during regular grabbing, with Parker slipping to the canvas multiple occasions during clinches.
Parker closed well, but several stanzas were difficult to score. However, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor advances, but with the caliber of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Hatton Tribute Fuels All-Manchester Fight
In the co-main event, Lyndon Arthur beat Rea by split-decision in a excellent all-Manchester fight to capture the continental championship.
The stadium grew hushed for a extremely emotional tribute before the fight as 10 bells tolled in honor of the city's native Ricky Hatton, who succumbed aged 46 in last month.
It was the premier televised match card in the location since Hatton's death. As the last bell faded, the quiet gave way to a roar of "only one Ricky Hatton".
The fighting within the ring matched the sentiment. Arthur was floored by a left hook flush on the chin in the initial stage, getting up unsteadily to his footing on the referee's count.
But the red-colored equipment of Arthur soon pressed ahead again. From the other corner, Rea - in competitive blue - was damaged quickly, significant bruising forming under his face as the duo traded punishing blows.
The challenger, 27, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the action hardly diminished over the full distance.
The victor barely secured the verdict with official scores of even score, narrow lead and wider gap, but each competitor were persistent and courageous, all the qualities their hero Hatton embodied.
