British light heavyweight Buatsi made a winning yet unimpressive beginning to his career under fresh promotional backing with a unanimous decision over Zach Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a split decision in a close ten-round fight at the boxing arena.
But Parker landed significant shots, connecting with powerful individual punches in a fight where the styles didn't complement each other, with frequent clinching spoiling the fight.
The scoring judges judged it 96-94 in favor to the winner, with the third a even score.
"It wasn't my finest display but what do champions do? They win," the victor said in the arena as he was faced boos from the crowd.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to secure a twentieth professional win.
Various analysts believed Parker, 31, deserved the decision but the contender suffered the second defeat of his 28-bout professional journey.
Buatsi Earns Victory in Dull Encounter
Buatsi's progress has stalled in the past few years through promotional disputes and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under fresh management.
He started carefully, with the two boxers willing to overcommit in a tentative early stages.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was participating in his second fight at the higher weight class.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who worked behind a solid defense to edge the cleaner periods.
The spectators' acceptance wore thin amid frequent holding, with the challenger going down various instances during grappling.
Parker finished the stronger, but many rounds were hard to judge. However, former world champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Memorial Inspires Manchester Derby Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a terrific all-Manchester battle to win the European light heavyweight belt.
The venue became quiet for a deeply poignant homage prior to the bout as 10 bells rang in memory of the city's native Ricky Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the concluding sound disappeared, the stillness became a shout of "there's only one Hatton".
The action inside the ropes equaled the emotion. Arthur was sent to the canvas by a powerful punch squarely on the face in the second round, standing uncertainly to his feet on the referee's count.
But the red-colored shorts of the fighter soon pressed ahead again. Across the ring, the opponent - in competitive blue - was damaged quickly, significant bruising appearing under his eye as the pair landed hard punches.
The challenger, 27, landed power punches but the champion, 34, matched the intensity with powerful upward punches as the action seldom decreased over twelve rounds.
The victor barely secured the decision with judges scorecards of draw, narrow lead and wider gap, but each competitor were relentless and brave, everything their hero Hatton embodied.
