Isco struck from the penalty spot for the 2-1 win on Saturday.
He said afterwards: "I'm exhausted, exhausted. In the end it's very difficult to win games, against Madrid, which has millions of resources, it's very difficult. We came out a little disconnected, letting them play too much and they hurt us.
"But halfway through the first half the team improved. Happy with the victory against the best team there is today. Hopefully we can end the year in the best possible way.
"It's very difficult, Madrid has the best players in the world, a million different resources, a lot of quality and a lot of speed, without the work of the whole team it would have been impossible.
"My wife was there, I'm recording a small documentary about how I'm recovering from my injury and I've asked for forgiveness from the Madrid fans, I'm always grateful for having helped me fulfil all the dreams that a child has and I always have Madrid in my heart."
On a Spain call-up, Isco added: "I owe my life to Betis, the national team is the dream of any player and I hope to have that opportunity again after six or seven years without going. I'm working to return one day."