British light heavyweight Buatsi earned a win yet unimpressive start to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a tight 10-round contest at the Co-op Live Arena.
But the challenger found success, connecting with powerful individual punches in a fight where the approaches never quite clicked, with constant grabbing spoiling the fight.
Two judges judged it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my finest display but what defines champions? They succeed," the victor said in the ring as he was met by boos from the crowd.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Some ringside observers believed Parker, thirty-one, deserved the decision but the Derbyshire fighter experienced the second defeat of his 28-match career.
Buatsi Claims Victory in Slow Match
His career development has stalled in the past few years through management issues and considerable time of inactivity.
Once tipped as the future of British boxing, he now stands trying to fulfil that early promise - perhaps in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers willing to take risks in a cagey opening few rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second appearance at light heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who utilized a protective stance to barely take the cleaner periods.
The spectators' acceptance wore thin amid frequent holding, with Parker slipping to the canvas several times during grappling.
The underdog finished the stronger, but many rounds were hard to judge. Nevertheless, ex-champion the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the presence of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Hatton Homage Fuels Local Rivalry Battle
In the co-main event, Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester contest to capture the European light heavyweight belt.
The venue became quiet for a profoundly moving memorial prior to the bout as 10 bells rang in honor of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the premier televised boxing event in the location since the passing of Hatton. As the last bell faded, the silence gave way to a roar of "only one Ricky Hatton".
The action within the ring equaled the sentiment. The eventual winner was knocked down by a significant blow squarely on the chin in the initial stage, getting up unsteadily to his feet on the eight count.
But the red-colored equipment of Arthur soon pressed ahead again. From the other corner, the opponent - in opposing blue - was damaged soon, significant bruising developing under his face as the fighters landed punishing blows.
The challenger, 27, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the intensity seldom decreased over the full distance.
Arthur edged the result with scoring tallies of even score, narrow lead and wider gap, but both fighters were persistent and full of heart, all the qualities their idol Hatton represented.
