UK light-heavyweight Buatsi earned a win yet underwhelming start to life under new promoters with a points victory over Zach Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a tight 10-round bout at the Manchester venue.
But Parker had his moments, connecting with powerful clean blows in a fight where the styles failed to mesh, with constant grabbing spoiling the action.
The scoring judges scored it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest performance but what defines champions? They succeed," Buatsi stated in the ring as he was greeted with boos from the spectators.
The Londoner bounced back after his initial pro loss - an epic battle with his previous opponent in February - to claim a 20th career victory.
Various analysts thought the challenger, 31, deserved the victory but the British boxer experienced the second defeat of his 28-match professional journey.
The Champion Secures Victory in Dull Encounter
His career development has plateaued in recent times through management issues and considerable time of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter willing to take risks in a cagey initial rounds.
Parker, whose sole prior loss came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second appearance at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a solid defense to edge the cleaner rounds.
The crowd's patience decreased during frequent holding, with the challenger going down several times during close exchanges.
The underdog closed well, but several stanzas were difficult to score. Nevertheless, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
The victor advances, but with the likes of hard hitter Benavidez, and Russian champion Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Tribute Fuels All-Manchester Contest
In the secondary fight, Arthur defeated Rea by divided decision in a excellent all-Manchester fight to secure the continental championship.
The stadium became quiet for a deeply poignant homage ahead of the contest as a bell ceremony tolled in remembrance of Manchester's own Ricky Hatton, who died 46 years old in September.
It was the first major televised fight night in the city since Hatton's passing. As the concluding sound faded, the stillness gave way to a roar of "only one Ricky Hatton".
The competition within the ring matched the sentiment. Arthur was sent to the canvas by a significant blow flush on the chin in the early round, getting up unsteadily to his position on the count of eight.
But the red-colored attire of Arthur soon pressed ahead again. From the other corner, the opponent - in rival City blue - was marked up early, heavy swelling forming under his orbital area as the fighters landed hard punches.
Rea, twenty-seven, landed power punches but the champion, 34, matched the intensity with effective uppercuts as the action hardly diminished over twelve rounds.
The victor barely secured the decision with judges scorecards of draw, 115-113 and wider gap, but the two athletes were relentless and full of heart, all the qualities their hero the legend represented.
