British light-heavyweight Buatsi earned a win yet unimpressive start to his career under new promoters with a unanimous decision over Zach Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a competitive ten-round fight at the boxing arena.
But Parker landed significant shots, connecting with powerful single shots in a fight where the approaches didn't complement each other, with excessive holding spoiling the contest.
Two judges had it 96-94 to the winner, with the third a 95-95.
"It wasn't my greatest performance but what defines champions? They win," the victor said in the arena as he was faced boos from the audience.
The Londoner got back to winning after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Various analysts thought Parker, thirty-one, merited the victory but the Derbyshire fighter suffered the second setback of his 28-fight professional journey.
The Champion Claims Victory in Dull Affair
The fighter's advancement has plateaued in the past few years through management issues and long spells of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under recent support.
He opened tentatively, with both competitors willing to overcommit in a cagey early stages.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who operated with a tight guard to narrowly win the better periods.
The spectators' acceptance wore thin amid regular grabbing, with Parker going down several times during grappling.
Parker closed well, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian champion Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Hatton Tribute Motivates Manchester Derby Contest
In the secondary fight, Lyndon Arthur defeated Bradley Rea by split-decision in a excellent Manchester vs Manchester fight to secure the European light-heavyweight belt.
The stadium fell silent for a profoundly moving memorial before the fight as a bell ceremony sounded in memory of the city's native Hatton, who died 46 years old in September.
It was the first major televised fight night in the urban center since the passing of Hatton. As the final chime disappeared, the quiet transitioned to a roar of "there's only one Ricky Hatton".
The competition during the bout reflected the sentiment. The eventual winner was floored by a significant blow squarely on the chin in the initial stage, standing uncertainly to his feet on the referee's count.
But the traditional red shorts of Arthur soon advanced again. On the opposite side, the opponent - in opposing blue - was marked up early, significant bruising developing under his face as the fighters exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the action seldom decreased over the full distance.
Arthur narrowly won the decision with official scores of 114-114, 115-113 and 115-112, but the two athletes were relentless and brave, exactly what their hero Hatton represented.
