UK light heavyweight Buatsi earned a win yet disappointing debut to life under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a competitive 10-round fight at the Co-op Live Arena.
But Parker landed significant shots, landing some telling clean blows in a fight where the techniques never quite clicked, with constant grabbing marring the action.
The officials judged it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They succeed," Buatsi said in the ring as he was met by boos from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Various analysts felt Parker, 31, deserved the victory but the Derbyshire fighter suffered the second setback of his 28-match professional journey.
Buatsi Secures Win in Slow Match
Buatsi's progress has stalled in recent years through management issues and considerable time of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what seems like a final roll of the dice - under fresh management.
He started carefully, with both competitors willing to overcommit in a calculated early stages.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was competing in only his second fight at the higher weight class.
By the halfway stage, Parker had kept it close, causing problems for Buatsi, who worked behind a protective stance to edge the better stanzas.
The audience's tolerance diminished during frequent holding, with Parker falling to the floor several times during close exchanges.
The underdog ended stronger, but several stanzas were challenging to assess. However, former world champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
The victor moves on, but with the caliber of power puncher David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Hatton Tribute Inspires Manchester Derby Fight
In the co-main event, Arthur defeated Rea by close verdict in a outstanding local rivalry contest to capture the continental championship.
The arena fell silent for a profoundly moving tribute before the fight as 10 bells rang in honor of local hero Ricky Hatton, who died 46 years old in last month.
It was the premier televised fight night in the city since Hatton's death. As the concluding sound faded, the silence became a shout of "there's just one Ricky Hatton".
The fighting during the bout reflected the emotion. The eventual winner was knocked down by a left hook squarely on the chin in the early round, rising shakily to his position on the eight count.
But the Manchester United-red shorts of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was marked up soon, heavy swelling appearing under his orbital area as the duo landed powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, matched the intensity with effective uppercuts as the action hardly diminished over 12 rounds.
Arthur barely secured the verdict with scoring tallies of 114-114, 115-113 and clearer margin, but each competitor were relentless and full of heart, exactly what their idol Hatton represented.
