Despite enjoying the majority share of possession, Spain were limited in their number of clear-cut chances, although David Villa came close after hitting the post and Cesc Fabregas squandered a late effort.
"It is a shame we didn't manage to win," said Casillas.
"It leaves a bitter taste because, in my personal opinion, it was not the right result.
"We created a few more chances than England, who showed their strength at a dead-ball situation and managed to convert something.
"Other than that, I can't really think that they created anything else throughout the game.
"The games we have found toughest to win have been against opponents who have set their stall out to work hard, run forever, close us down and really try and keep things tight in the middle of the pitch."