Hull City boss Phil Brown was angry over Liverpool's opening goal in yesterday's 3-1 defeat.
Brown claimed his side had suffered an "injustice" after Javier Mascherano was awarded the free-kick on the edge of the area that led to the opening goal.
Xabi Alonso's initial effort from the set-piece struck the wall but the Spaniard lashed the rebound home.
"It was clear," Benitez said. "Mascherano was going down and the other player [George Boateng] kicked him."