Redknapp told reporters: "A few minutes before half-time we were 1-0 down and still bang in the game.
"To come in at 3-0 down, when our keeper has not had a shot to save [is hard to take]. If you have ever played in a team 3-0 down at half-time it is very difficult. You have to make sure you don't get beat by six or seven.
"[It was] a difficult day, I expected it and we got one."
The defeat leaves QPR 16th in the Premier League table with three points from their opening four games.