However, Cooper thought that goalkeeper Joe Lewis's performance didn't warrant the Posh keeper conceding four goals.
"The goalkeeper kept us in it in the first half. He didn't deserve to concede four goals with his performance," Cooper said after the 4-0 defeat.
"We thought Harry [Redknapp] might rest a few but it wasn't to be. He probably wants to keep the continuity going and rightly so and they were too good for us today.
"It was a fantastic performance from them. I was really impressed.
"They are a really good team. "I think they will finish in the top four.
"I said to the players 'You are playing against some of the best in Europe today go and enjoy it, test yourselves'.
"I can't fault the effort from the players. We just didn't defend. The goals were too soft."