Athletic won 2-0 via goals through Inaki Williams and Oihan Sancet.
Valverde said afterwards: "It was a great game in my opinion. The atmosphere was full of excitement about playing a European game in Bilbao and the team responded well, putting in pace and drive. We were able to open up their defence, which was difficult for us because we value our opponents too much.
"Nico (Williams) is a treasure and an insurance for us. He is always persevering and is brave when facing the opposition, as well as always looking at goal. He is a very high level player because he has speed, definition and dribbling. We know what we have, but we give him normality because we have seen him for years and living normally is the best way for him to be comfortable."
He also explained: "The first twenty minutes of the first half were the best of the season, but the same intention we have to attack always betrays us and makes us rush. At half-time we talked about calming down a bit because we had already had some losses at the start and we wanted to get closer to the top zone."