British light heavyweight Buatsi secured a victory yet underwhelming start to life under fresh promotional backing with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a tight 10-round fight at the Manchester venue.
But the challenger landed significant shots, connecting with powerful clean blows in a match 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 final judge a even score.
"It wasn't my finest showing but what do champions do? They succeed," the victor commented in the arena as he was faced disapproval from the crowd.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in last winter - to claim a 20th career victory.
Various analysts felt the challenger, thirty-one, deserved the victory but the contender endured the second setback of his 28-fight career.
Buatsi Earns Triumph in Dull Affair
His career development has slowed in recent years through promotional disputes and long spells of inactivity.
Once tipped as the next star of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with both competitors ready to overcommit in a tentative opening few rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after damaging his hand during the bout, was making just his second bout at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who worked behind a tight guard to barely take the more effective periods.
The audience's tolerance wore thin because of regular grabbing, with Parker falling to the floor several times during clinches.
Parker ended stronger, but many rounds were hard to judge. However, previous titleholder Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor progresses, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - judging by this showing - still seems difficult.
Hatton Tribute Inspires Local Rivalry Fight
In the secondary fight, Arthur beat Rea by split-decision in a outstanding all-Manchester fight to win the continental belt.
The arena fell silent for a deeply poignant tribute ahead of the contest as 10 bells rang in remembrance of the city's native Ricky Hatton, who passed away aged 46 in September.
It was the initial significant broadcast fight night in the urban center since Hatton's passing. As the final chime faded, the silence transitioned to a shout of "there's only one Ricky Hatton".
The action inside the ropes equaled the sentiment. Arthur was knocked down by a left hook directly to the jaw in the initial stage, standing uncertainly to his position on the referee's count.
But the Manchester United-red shorts of the fighter soon came forward again. On the opposite side, the opponent - in competitive blue - was damaged quickly, noticeable damage forming under his orbital area as the pair exchanged punishing blows.
Rea, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with stinging uppercuts as the intensity hardly diminished over the full distance.
Arthur narrowly won the decision with scoring tallies of 114-114, close margin and 115-112, but each competitor were relentless and courageous, everything their inspiration the legend stood for.
