Real won the first-leg of the round of 16 tie 1-0 thanks to Ferland Mendy's winner.
Nacho said, "It was tough but we eventually got the goal.
"The objective is always to keep a clean sheet away from home, we're defending really well and even if they were down to ten, it's never easy.
"We've been able to score and also keep a clean sheet which means a lot. You need to give the boys all the credit with what we're going. We wanted to score more, to tell you the truth."