Vini Jr hit a hat-trick and Jude Bellingham also scored as Real were comfortable winners.
Pendin later said: “The truth is that when you come to a stage like this, against an opponent hurt after two defeats, we had to give our best version, and we didn't. The counterattacks hurt us a lot and we had talked about it. It hurts us for our people who came.
"The game was under control but we could have done a lot more in the first half. Real Madrid can do a lot of damage with their punch. We had to have played a perfect game and it wasn't like tha.
“The third goal killed the match . We thought that if we scored 2-1, we would be in it. But that wasn't the case and the third goal sealed the deal for us.
“We are 5th for a reason, we had to give our best. It was a great opportunity but we were unable to hurt them. We should have attacked more on the wings and until the first goal we hadn't had any problems. We have to get this out of our heads and reset."
Regarding the approach, he explaine : “We wanted to be in a low block because Madrid forces you to. We wanted to counterattack and it worked for us until the first goal. The first goal marked the game but we were in it. Maybe the second goal was key. I think the approach was not bad.”