A late penalty converted by Ross Stewart saw Saints win the fifth round tie today.
Silva, on his selection, said: "I understand that, it's more than that. It was a bad afternoon for us and for our fans. We need to look deeper because I'm not pleased at all what has happened this afternoon.
"This one is more than a defeat - if it's because of the changes then fine, I get it - but (Ryan) Sessegnon and (Timothy) Castagne have played this season against top Premier League sides, Oscar Bobb and Samuel Chukwueze are at the level. We have to look deeper. I understand that I get the blame for making the changes.
"For me it's simple, when you have 24 shots and they don't have many clear-cut chances. We arrived in their box, created from the sides but with end product we have to finish, have to be quicker and arrive in the right spots in the box.
"They have five shots and have chances to score, any moment on the counter was a chance for them. It's about mindset. When you have so many shots and looking for the chances we should've created more. The end product of our team was not the level it should be."
On picking things up for the rest of season, Silva added: "It's our obligation, we have to understand it was a very, very bad afternoon. We know anything can happen on football but it's more than that. We have to look deeper because it was not good enough and that starts with me looking at myself."