Luis Diaz scored twice, with Mohamed Salah also struck for the visitors' win.
Ten Hag said, "We made mistakes and they were very clinical in finishing. They did very well.
"If I see all the chances we conceded, I don't think that's what happened. We made mistakes. It was all individual errors. Maybe the last one you can debate where our double-six was. Liverpool did brilliant but the goals conceded expectations were not that high.
"It's clear Liverpool deserved the win. We have to be humble, take this and improve our game."
On Casemiro being taken off at halftime, he said: "It is what the team needed. You know when you are 2-0 down against Liverpool you have to take more risks, it will be open. When you are losing you have to take more risks. I have to give compliments to the team. You have to keep fighting and sticking together.
"You know the game and he knows the game. He will go on and we will go on. He's a great player. We will continue this season to improve the team and the players.
"He improved and has shown so often that he is a great character. We all have seen great moments from him and him be decisive in midfield. He will show that again and will bounce back."
Ten Hag also said, "I don't think we are in the same pattern. It was sometimes open and we took risks. But I don't want to talk about this after a 3-0 defeat to Liverpool. Well done Liverpool. We have to be humble and take it.
"There are many games to play and I know where we will be at the end of the season. We will go for trophies. That will stand."
On if the team is improving, Ten Hag also said: "In the two years, we took two prizes. We will see where we are at the end of the season. We brought new players in. There are still some players not available. The opponent is probably a little bit further in certain areas but we will catch up and come back. I don't want to talk about good things today. We lost 3-0. We have to stand up and bounce back."