British light heavyweight Buatsi made a winning yet disappointing start to life under new promoters with a decision win over Zach Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a majority decision in a close 10-round fight at the Co-op Live Arena.
But Parker found success, connecting with powerful individual punches in a fight where the approaches never quite clicked, with frequent clinching spoiling the action.
The scoring judges had it 96-94 to the winner, with the third a 95-95.
"It wasn't my best performance but what do champions do? They prevail," the victor stated in the ringside as he was met by disapproval from the audience.
The Londoner got back to winning after his maiden career setback - an memorable fight with his previous opponent in February - to earn a 20th pro success.
Several boxing experts thought Parker, thirty-one, should have been awarded the decision but the British boxer endured the second setback of his 28-bout professional journey.
The Champion Secures Triumph in Uneventful Match
The fighter's advancement has slowed in recent years through management issues and considerable time of inactivity.
Once tipped as the rising talent of UK boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a final roll of the dice - under fresh management.
He started carefully, with the two boxers willing to be aggressive in a cagey initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was making just his second bout at the higher weight class.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who operated with a solid defense to barely take the cleaner rounds.
The spectators' acceptance diminished amid constant clinching, with Parker slipping to the canvas various instances during clinches.
Parker finished the stronger, but multiple periods were difficult to score. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor moves on, but with the presence of power puncher David Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Hatton Memorial Inspires Local Rivalry Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a outstanding all-Manchester fight to win the European light-heavyweight title.
The arena fell silent for a extremely emotional tribute prior to the bout as a bell ceremony rang in honor of Manchester's own Ricky Hatton, who succumbed aged 46 in last month.
It was the first major televised fight night in the location since Hatton's death. As the final chime disappeared, the quiet gave way to a chant of "there's just one Hatton".
The fighting within the ring matched the emotion. Arthur was sent to the canvas by a left hook squarely on the chin in the second round, rising shakily to his feet on the eight count.
But the traditional red equipment of Arthur soon came forward again. From the other corner, the opponent - in competitive blue - was injured early, heavy swelling forming under his orbital area as the duo traded hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with stinging uppercuts as the intensity hardly diminished over twelve rounds.
Arthur narrowly won the result with scoring tallies of even score, 115-113 and wider gap, but both fighters were persistent and full of heart, exactly what their inspiration the legend stood for.
