British light heavyweight Buatsi secured a victory yet disappointing start to life under new promoters with a points victory over Zach Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a competitive ten-round bout at the Manchester venue.
But the challenger had his moments, delivering effective clean blows in a contest where the techniques never quite clicked, with frequent clinching spoiling the fight.
Two judges scored it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my best showing but what do champions do? They succeed," Buatsi stated in the ring as he was faced disapproval from the crowd.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts believed Parker, 31, should have been awarded the decision but the contender endured the second loss of his 28-fight career.
The Champion Secures Triumph in Slow Encounter
The fighter's advancement has plateaued in the past few years through promotional disputes and considerable time of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to realize his potential - perhaps in what feels like a last chance - under fresh management.
He opened tentatively, with both competitors willing to be aggressive in a cagey initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was making just his second fight at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who operated with a solid defense to edge the cleaner periods.
The crowd's patience diminished amid regular grabbing, with the challenger slipping to the canvas multiple occasions during clinches.
Parker ended stronger, but multiple periods were challenging to assess. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor advances, but with the presence of hard hitter David Benavidez, and Russian champion Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Tribute Inspires All-Manchester Contest
In the supporting bout, Lyndon Arthur overcame Rea by close verdict in a excellent all-Manchester fight to capture the European light heavyweight belt.
The stadium became quiet for a extremely emotional memorial before the fight as a bell ceremony rang in memory of the city's native Ricky Hatton, who died at age 46 in September.
It was the first major televised match card in the city since Hatton's death. As the concluding sound faded, the silence gave way to a roar of "there's just one Hatton".
The fighting inside the ropes equaled the emotion. The eventual winner was knocked down by a left hook squarely on the chin in the second round, getting up unsteadily to his feet on the referee's count.
But the red-colored equipment of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was injured quickly, significant bruising developing under his orbital area as the duo landed powerful shots.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with stinging uppercuts as the action rarely dropped over twelve rounds.
Arthur barely secured the verdict with scoring tallies of 114-114, narrow lead and wider gap, but each competitor were persistent and brave, everything their inspiration Hatton represented.
