Pena kept a clean sheet as Barca extended their lead at the top of the table with this rout.
He later said: "The team is doing some spectacular work. We played 48 hours ago... We scored four goals and in the second half we could have faltered... In the end we are a group of 23-24 who are feeling like a team. I am very happy.
"(Wojciech) Sczezcny showed me respect from the first day that perhaps I didn't deserve... But as a person he is spectacular, he always helped me. We are a team, we work hard together. In the first half we were a bit out of control, with too much direct play, but when Frenkie (De Jong) came on we found Madrid's back.
"In the end I am not making any claims, I want to play as much as possible in the best way. I demanded more of myself than anyone else to be able to be good, and even if you win everything looks much better."