UK light heavyweight Buatsi earned a win yet unimpressive debut to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a tight ten-round bout at the boxing arena.
But the challenger had his moments, delivering effective individual punches in a contest where the approaches never quite clicked, with constant grabbing marring the contest.
The officials scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best display but how do champions respond? They succeed," the victor said in the ring as he was met by negative reactions from the spectators.
The Londoner got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to secure a twentieth professional win.
Various analysts believed the challenger, thirty-one, should have been awarded the decision but the Derbyshire fighter suffered the second defeat of his 28-match career.
The Champion Secures Victory in Slow Affair
His career development has stalled in recent years through promotional disputes and considerable time of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to achieve expectations - maybe in what feels like a ultimate opportunity - under recent support.
He opened tentatively, with neither fighter ready to overcommit in a calculated early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in 2022 after breaking his hand in the contest, was competing in only his second bout at light heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a protective stance to edge the more effective periods.
The audience's tolerance diminished amid constant clinching, with Parker going down multiple occasions during close exchanges.
The underdog finished the stronger, but multiple periods were difficult to score. Although, ex-champion Carl Frampton - working with Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of power puncher Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Homage Fuels All-Manchester Battle
In the secondary fight, Arthur overcame Bradley Rea by divided decision in a terrific Manchester vs Manchester contest to win the European light heavyweight championship.
The venue became quiet for a deeply poignant memorial prior to the bout as 10 bells tolled in honor of local hero Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the final chime ended, the silence became a roar of "there's just one Hatton".
The action during the bout reflected the emotion. The eventual winner was sent to the canvas by a significant blow squarely on the face in the initial stage, standing uncertainly to his position on the eight count.
But the red-colored shorts of Arthur soon advanced again. Across the ring, the opponent - in competitive blue - was injured soon, heavy swelling appearing under his eye as the pair exchanged hard punches.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace seldom decreased over the full distance.
The victor narrowly won the result with judges scorecards of 114-114, narrow lead and clearer margin, but the two athletes were determined and brave, exactly what their inspiration the legend stood for.
