British light heavyweight Buatsi made a winning yet disappointing start to his career under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a competitive 10-round contest at the boxing arena.
But Parker found success, landing some telling clean blows in a contest where the techniques never quite clicked, with constant grabbing marring the action.
The scoring judges had it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my finest performance but what defines champions? They prevail," the victor said in the arena as he was met by boos from the audience.
The Londoner got back to winning after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers thought Parker, 31, merited the decision but the British boxer experienced the second setback of his 28-bout career.
The Champion Claims Win in Dull Encounter
His career development has plateaued in recent years through promotional disputes and considerable time of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with both competitors ready to overcommit in a tentative early stages.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a protective stance to barely take the better stanzas.
The crowd's patience wore thin because of frequent holding, with Parker going down multiple occasions during grappling.
The underdog closed well, but multiple periods were challenging to assess. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it strongly leaning for the challenger, giving Buatsi just one round.
The victor moves on, but with the likes of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels All-Manchester Contest
In the secondary fight, Lyndon Arthur overcame Rea by close verdict in a excellent all-Manchester contest to capture the European light heavyweight title.
The venue became quiet for a profoundly moving homage prior to the bout as ten bells rang in memory of Manchester's own Ricky Hatton, who succumbed at age 46 in September.
It was the premier televised boxing event in the city since Hatton's death. As the final chime ended, the silence transitioned to a shout of "there's only one Hatton".
The competition during the bout matched the sentiment. Arthur was sent to the canvas by a significant blow directly to the face in the second round, rising shakily to his feet on the count of eight.
But the Manchester United-red shorts of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was injured early, noticeable damage appearing under his orbital area as the duo exchanged hard punches.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the pace hardly diminished over twelve rounds.
The victor barely secured the result with scoring tallies of even score, narrow lead and wider gap, but each competitor were persistent and full of heart, exactly what their idol Hatton embodied.
