British light heavyweight Buatsi made a winning yet disappointing start to his career under new promoters with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a competitive 10-round bout at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful individual punches in a contest where the styles didn't complement each other, with frequent clinching disrupting the fight.
The officials judged it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest performance but what defines champions? They win," Buatsi commented in the ringside as he was faced negative reactions from the crowd.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to secure a 20th pro success.
Various analysts felt Parker, thirty-one, merited the win but the Derbyshire fighter experienced the second loss of his 28-match career.
Buatsi Claims Win in Uneventful Encounter
The fighter's advancement has stalled in recent years through contract problems and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under recent support.
He opened tentatively, with neither fighter ready to overcommit in a calculated 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 in the contest, was participating in his second fight at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, causing problems for Buatsi, who worked behind a solid defense to barely take the more effective rounds.
The crowd's patience wore thin because of regular grabbing, with the challenger falling to the floor various instances during clinches.
Parker finished the stronger, but multiple periods were challenging to assess. Nevertheless, previous titleholder the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi moves on, but with the likes of power puncher Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Tribute Fuels Local Rivalry Fight
In the supporting bout, Lyndon Arthur beat Rea by close verdict in a outstanding local rivalry contest to win the European light-heavyweight belt.
The venue became quiet for a deeply poignant memorial prior to the bout as ten bells sounded in remembrance of the city's native Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast match card in the location since Hatton's death. As the last bell faded, the silence gave way to a shout of "there's only one Ricky Hatton".
The competition inside the ropes reflected the sentiment. The eventual winner was knocked down by a left hook directly to the chin in the second round, standing uncertainly to his footing on the count of eight.
But the traditional red equipment of Arthur soon advanced again. Across the ring, Rea - in rival City blue - was marked up early, significant bruising forming under his eye as the duo landed hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the intensity rarely dropped over twelve rounds.
The victor narrowly won the verdict with official scores of draw, 115-113 and clearer margin, but both fighters were persistent and courageous, all the qualities their inspiration the legend represented.
