The former Tottenham midfielder was an 83rd minute substitute in the 2-1 second-leg win.
"I am very happy. I know I could not start," he acknowledged. "I thank the fans for the love you have given me. I understood my new teammates very easily.
"I know the expectations are high for this team. Now I work very hard to help this team. I have not been nervous.
"I noticed that Spanish football is more technical than the English."