UK light-heavyweight Buatsi made a winning yet disappointing debut to his career under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a tight ten-round fight at the Manchester venue.
But Parker landed significant shots, landing some telling individual punches in a contest where the techniques didn't complement each other, with excessive holding disrupting the action.
The scoring judges judged it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my greatest showing but what do champions do? They succeed," the victor commented in the ring as he was faced boos from the crowd.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to secure a 20th career victory.
Some ringside observers thought the challenger, 31, merited the victory but the contender experienced the second loss of his 28-bout career.
The Champion Earns Win in Dull Match
The fighter's advancement has stalled in recent times through contract problems and long spells of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to achieve expectations - maybe in what feels like a last chance - under recent support.
He opened tentatively, with the two boxers ready to overcommit in a calculated early stages.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was competing in only his second fight at the higher weight class.
By the middle rounds, Parker had made it competitive, creating difficulties for Buatsi, who operated with a solid defense to narrowly win the more effective periods.
The audience's tolerance diminished amid frequent holding, with the challenger falling to the floor multiple occasions during close exchanges.
Parker closed well, but many rounds were difficult to score. Nevertheless, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Russian star Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Hatton Tribute Motivates All-Manchester Fight
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a outstanding all-Manchester battle to win the continental championship.
The arena became quiet for a extremely emotional homage prior to the bout as ten bells tolled in honor of local hero Ricky Hatton, who died at age 46 in last month.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the final chime disappeared, the stillness transitioned to a chant of "there's just one Ricky Hatton".
The competition inside the ropes equaled the emotion. Arthur was floored by a significant blow squarely on the jaw in the second round, getting up unsteadily to his feet on the eight count.
But the red-colored equipment of the fighter soon advanced again. Across the ring, Rea - in opposing blue - was marked up soon, heavy swelling appearing under his orbital area as the duo exchanged powerful shots.
The challenger, twenty-seven, landed power punches but the champion, 34, matched the intensity with effective uppercuts as the action hardly diminished over 12 rounds.
The victor barely secured the verdict with scoring tallies of 114-114, 115-113 and wider gap, but the two athletes were determined and courageous, everything their inspiration Hatton embodied.
