UK light-heavyweight Buatsi made a winning yet disappointing start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a tight 10-round fight at the boxing arena.
But Parker had his moments, delivering effective single shots in a match where the techniques didn't complement each other, with excessive holding marring the action.
The scoring judges scored it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my greatest display but how do champions respond? They win," the victor said in the ring as he was faced negative reactions from the crowd.
The British fighter returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to secure a 20th career victory.
Some ringside observers believed Parker, thirty-one, should have been awarded the win but the Derbyshire fighter experienced the second defeat of his 28-bout professional journey.
The Champion Secures Win in Uneventful Encounter
His career development has stalled in the past few years through contract problems and considerable time of lack of fights.
Previously predicted as the future of UK boxing, he now is positioned trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with both competitors ready to be aggressive in a tentative initial rounds.
Parker, whose sole prior loss came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was making just his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for the favorite, who operated with a tight guard to barely take the better periods.
The spectators' acceptance decreased during regular grabbing, with the challenger falling to the floor various instances during grappling.
The underdog ended stronger, but several stanzas were difficult to score. Nevertheless, ex-champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the presence of hard hitter Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - based on this performance - still looks steep.
Hatton Homage Motivates Local Rivalry Battle
In the supporting bout, Arthur defeated Bradley Rea by close verdict in a excellent Manchester vs Manchester fight to capture the European light heavyweight title.
The arena became quiet for a profoundly moving homage prior to the bout as 10 bells rang in honor of Manchester's own Ricky Hatton, who passed away aged 46 in September.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the last bell faded, the stillness gave way to a shout of "there's only one Hatton".
The fighting during the bout reflected the feeling. The eventual winner was sent to the canvas by a left hook squarely on the face in the early round, standing uncertainly to his footing on the eight count.
But the red-colored equipment of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was marked up quickly, significant bruising appearing under his orbital area as the pair traded punishing blows.
Rea, 27, connected with strong blows but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity hardly diminished over the full distance.
Arthur barely secured the decision with official scores of draw, close margin and clearer margin, but each competitor were relentless and courageous, everything their inspiration Hatton embodied.
