Second-half strikes from Gareth Bale and Cristiano Ronaldo cancelled out Arturo Vidal's penalty, before Fernando Llorente evened things up, but Casillas said that he was pleased with the point in Italy.
"I'm very happy, it's always difficult to play in these type of games," he told reporters.
"You have to be at your very best if the coach is to trust you. I only play once every two weeks.
"We are doing very well, 10 points out of 12 is good. Now we must improve in La Liga and try to reduce the gap with Barcelona and Atletico Madrid."
The draw leaves Madrid top of Group B with 10 points from four games.