UK light heavyweight Buatsi earned a win yet disappointing debut to life under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a split decision in a tight ten-round bout at the Manchester venue.
But Parker landed significant shots, landing some telling single shots in a fight where the approaches failed to mesh, with frequent clinching disrupting the action.
Two judges scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my best display but how do champions respond? They win," the victor commented in the ring as he was faced boos from the spectators.
The Londoner got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a 20th pro success.
Various analysts believed Parker, thirty-one, should have been awarded the win but the Derbyshire fighter endured the second defeat of his 28-fight professional journey.
The Champion Claims Win in Uneventful Match
The fighter's advancement has slowed in recent years through promotional disputes and long spells of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under new promotional backing.
He started carefully, with neither fighter prepared to take risks in a tentative opening few rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after breaking his hand during the bout, was making just his second fight at the higher weight class.
By the fight's midpoint, Parker had made it competitive, making life awkward for the favorite, who operated with a solid defense to barely take the more effective periods.
The spectators' acceptance decreased amid frequent holding, with Parker slipping to the canvas several times during close exchanges.
The underdog finished the stronger, but many rounds were challenging to assess. However, previous titleholder Carl Frampton - working with the broadcast network - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Hatton Homage Fuels Manchester Derby Contest
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a outstanding local rivalry fight to secure the European light-heavyweight belt.
The arena grew hushed for a deeply poignant homage before the fight as 10 bells sounded in honor of the city's native Ricky Hatton, who passed away at age 46 in September.
It was the first major televised boxing event in the city since Hatton's death. As the concluding sound faded, the stillness transitioned to a chant of "there's just one Hatton".
The action within the ring matched the feeling. Arthur was sent to the canvas by a powerful punch flush on the jaw in the second round, standing uncertainly to his position on the eight count.
But the traditional red attire of Arthur soon advanced again. Across the ring, Rea - in competitive blue - was damaged quickly, heavy swelling developing under his eye as the pair exchanged punishing blows.
Rea, twenty-seven, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the intensity seldom decreased over 12 rounds.
The victor barely secured the result with scoring tallies of even score, 115-113 and wider gap, but the two athletes were determined and brave, exactly what their idol Hatton stood for.
