Karanka admitted his side had not been at their best for long periods in the game, but was left to rue two late penalty decisions which did not go his side's way as first Scott Dann and then Damien Delaney survived handball claims.
Karanka said: "I don't need to say anything. You said it was handball and I think everybody could see both of them so for that reason, I don't need to say anything, just to say that today we have lost from mistakes.
"We have lost and we have to learn because today has been a good example that if we don't play with our intensity, we are in the Premier League and we are going to pay for mistakes.
"If we arrived today unbeaten, it's because we played the first three games with an amazing intensity and today, especially in the first half, we didn't play with that intensity.
"In the second half, we had chances, we had a lot of things, but again it's a good game to learn that we can't drop our intensity for one second in the Premier League."
Asked if his players would learn from a sobering experience, Karanka added: "I hope so because for sure I have learnt.
"They are intelligent and for sure they have learnt that we have to play in the way we played the first three games and in the way that we played the second half today."