British light heavyweight Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a tight ten-round fight at the Manchester venue.
But Parker had his moments, delivering effective clean blows in a fight where the approaches didn't complement each other, with frequent clinching spoiling the action.
The scoring judges judged it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my finest display but what defines champions? They win," the victor commented in the arena as he was met by disapproval from the crowd.
The British fighter bounced back after his maiden career setback - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Various analysts thought Parker, 31, deserved the victory but the British boxer endured the second loss of his 28-fight professional journey.
Buatsi Earns Triumph in Uneventful Match
Buatsi's progress has plateaued in the past few years through contract problems and extended periods of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what seems like a last chance - under new promotional backing.
He started carefully, with the two boxers ready to be aggressive in a calculated opening few rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand in the contest, was making just his second bout at the higher weight class.
By the halfway stage, the underdog had kept it close, making life awkward for Buatsi, who operated with a protective stance to edge the better rounds.
The audience's tolerance decreased because of frequent holding, with the challenger falling to the floor various instances during clinches.
The underdog finished the stronger, but several stanzas were hard to judge. However, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
Buatsi moves on, but with the likes of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Hatton Tribute Inspires Manchester Derby Battle
In the co-main event, Lyndon Arthur beat Rea by divided decision in a terrific local rivalry contest to secure the European light heavyweight title.
The arena grew hushed for a profoundly moving homage prior to the bout as 10 bells rang in honor of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised fight night in the location since Hatton's death. As the last bell disappeared, the quiet gave way to a chant of "there's just one Ricky Hatton".
The competition during the bout matched the emotion. Arthur was floored by a powerful punch directly to the face in the second round, getting up unsteadily to his position on the referee's count.
But the traditional red equipment of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was marked up early, heavy swelling appearing under his face as the pair exchanged hard punches.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with powerful upward punches as the intensity rarely dropped over 12 rounds.
Arthur narrowly won the verdict with official scores of 114-114, close margin and clearer margin, but each competitor were determined and courageous, everything their inspiration the legend embodied.
