British light-heavyweight Buatsi made a winning yet unimpressive start to life under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a majority decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker had his moments, delivering effective clean blows in a contest where the approaches never quite clicked, with excessive holding marring the action.
Two judges scored it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my best performance but what defines champions? They succeed," the victor stated in the ring as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a 20th career victory.
Various analysts thought Parker, 31, deserved the victory but the British boxer endured the second setback of his 28-bout professional journey.
The Champion Secures Victory in Uneventful Match
The fighter's advancement has plateaued in recent years through promotional disputes and long spells of inactivity.
Once tipped as the future of British boxing, he now stands trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter prepared to overcommit in a calculated early stages.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was participating in his second fight at light-heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for Buatsi, who utilized a protective stance to edge the cleaner stanzas.
The audience's tolerance decreased amid frequent holding, with Parker going down multiple occasions during close exchanges.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Memorial Motivates Manchester Derby Battle
In the supporting bout, Lyndon Arthur beat Rea by close verdict in a excellent Manchester vs Manchester fight to capture the continental belt.
The venue grew hushed for a extremely emotional homage before the fight as a bell ceremony rang in honor of Manchester's own Ricky Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the final chime faded, the stillness gave way to a chant of "only one Ricky Hatton".
The fighting within the ring reflected the feeling. The eventual winner was floored by a left hook flush on the face in the early round, getting up unsteadily to his footing on the referee's count.
But the traditional red attire of Arthur soon came forward again. From the other corner, Rea - in opposing blue - was damaged early, noticeable damage developing under his face as the pair exchanged punishing blows.
The challenger, 27, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the intensity rarely dropped over 12 rounds.
The victor barely secured the verdict with scoring tallies of draw, close margin and clearer margin, but both fighters were relentless and full of heart, exactly what their inspiration Hatton embodied.
