British light-heavyweight Buatsi secured a victory yet underwhelming debut to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a tight 10-round bout at the Co-op Live Arena.
But Parker had his moments, landing some telling clean blows in a contest where the styles never quite clicked, with frequent clinching spoiling the action.
The officials had it 96-94 to Buatsi, with the final judge a 95-95.
"It wasn't my best showing but how do champions respond? They win," the victor said in the ring as he was greeted with disapproval from the audience.
The Londoner bounced back after his first professional defeat - an epic battle with his previous opponent in last winter - to claim a twentieth professional win.
Various analysts felt Parker, thirty-one, merited the decision but the British boxer endured the second defeat of his 28-bout career.
The Champion Claims Victory in Dull Match
The fighter's advancement has stalled in recent times through contract problems and considerable time of inactivity.
Once tipped as the future of the British fight scene, he now is positioned trying to achieve expectations - possibly in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter prepared to overcommit in a tentative early stages.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for Buatsi, who utilized a solid defense to edge the better rounds.
The crowd's patience wore thin because of frequent holding, with Parker slipping to the canvas multiple occasions during close exchanges.
Parker finished the stronger, but many rounds were difficult to score. However, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just a single round.
Buatsi moves on, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Memorial Motivates Local Rivalry Contest
In the co-main event, Arthur beat Rea by close verdict in a outstanding Manchester vs Manchester fight to secure the European light heavyweight belt.
The stadium became quiet for a profoundly moving tribute prior to the bout as ten bells rang in honor of local hero Hatton, who died 46 years old in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the concluding sound disappeared, the silence became a chant of "there's just one Ricky Hatton".
The competition during the bout matched the sentiment. Arthur was knocked down by a significant blow squarely on the jaw in the initial stage, standing uncertainly to his position on the count of eight.
But the red-colored attire of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was injured quickly, noticeable damage forming under his eye as the fighters traded hard punches.
The challenger, 27, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the intensity seldom decreased over the full distance.
Arthur narrowly won the verdict with judges scorecards of 114-114, 115-113 and wider gap, but each competitor were relentless and full of heart, everything their idol the legend represented.
