UK light heavyweight Buatsi made a winning yet disappointing start to his career under recent management with a points victory over Zach Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a majority decision in a close 10-round bout at the boxing arena.
But Parker found success, landing some telling single shots in a contest where the techniques failed to mesh, with excessive holding marring the action.
The scoring judges had it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my best display but what do champions do? They win," Buatsi said in the ring as he was greeted with boos from the audience.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in February - to claim a 20th career victory.
Some ringside observers thought Parker, 31, merited the victory but the Derbyshire fighter experienced the second defeat of his 28-bout professional journey.
The Champion Earns Triumph in Dull Encounter
His career development has stalled in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the next star of the British fight scene, he now stands trying to realize his potential - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors prepared to be aggressive in a cagey initial rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second bout at the higher weight class.
By the middle rounds, the underdog had stayed in contention, causing problems for the favorite, who worked behind a tight guard to edge the more effective stanzas.
The crowd's patience diminished amid constant clinching, with Parker slipping to the canvas several times during grappling.
Parker finished the stronger, but several stanzas were challenging to assess. However, former world champion the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, giving Buatsi just one round.
The victor moves on, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Hatton Homage Inspires All-Manchester Fight
In the supporting bout, Lyndon Arthur beat Rea by divided decision in a terrific local rivalry contest to win the European light heavyweight belt.
The venue became quiet for a profoundly moving memorial prior to the bout as 10 bells tolled in remembrance of Manchester's own Hatton, who succumbed aged 46 in last month.
It was the premier televised fight night in the location since the passing of Hatton. As the concluding sound faded, the quiet transitioned to a chant of "there's only one Ricky Hatton".
The action during the bout equaled the emotion. The eventual winner was knocked down by a significant blow squarely on the jaw in the early round, getting up unsteadily to his feet on the eight count.
But the Manchester United-red shorts of the fighter soon advanced again. Across the ring, Rea - in opposing blue - was damaged early, noticeable damage appearing under his face as the fighters landed punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with powerful upward punches as the action seldom decreased over 12 rounds.
The victor narrowly won the decision with scoring tallies of even score, 115-113 and clearer margin, but the two athletes were relentless and full of heart, exactly what their idol Hatton represented.
