They went a goal behind when Kevin Davies gave the Trotters the lead, but were unlucky when a Luis Garcia goal was wrongly ruled offside by the linesman.
"In our opinion it is a goal. We have seen the TV and it is a goal," said Benitez.
"I thought we played okay in the first half and had three good opportunities to score, and in the second half we had a great chance at the end with Cisse.
"To lose Sami in the first half was important for us. He is good in the air and all the game the ball in the area was in the air and it is difficult."
