The 24-year-old netted Madrid's final goal in Sunday night's 4-1 victory as they regained their eight-point lead at the top of La Liga.
"We played good football to get this victory," he said. "I came on and I used my freshness to score the goal. I got a wonderful pass.
"Now we have to think about the Copa del Rey match as something very important. It will be very hard but we can win if we play like this."
Madrid take a 2-1 deficit to the Nou Camp on Wednesday evening.