"It was a really intense game," the 29-year-old Spaniard told reporters.
"From start to finish, there was a lot of pace to the game. It was a worthy quarter-final. Atletico are really strong and the tie remains open.
"I don't know what percentage of options we have to get through, but [the second leg] will be another very even game. This is a good thing, knowing that we must compete and take these challenges on."
The second leg of the tie will take place at the Vicente Calderon next week.