The Reds fell behind midway through the first half then twice more in five minutes after the break in a disappointing display.
Head coach Stendel said: “None of us expected this performance. In the end Carlisle won 3-0 and deserved to win 3-0. It is hard for us today. We thought this team was good enough to win this game but they did not show enough quality as a team. We missed a lot of things.
“We made too many mistakes and lost a lot of easy balls. We said after the Sheffield Wednesday game (a 2-0 Championship loss on Saturday) that we want to play more as a team and play our game and I didn’t get the impression tonight that we have emotion on the pitch.
“You can expect more fight, especially when you are the favourites at home with 5,000 people in the stand. I feel let down now but after I sleep I will look forward to the game on Saturday.
“It is very difficult to explain why we showed this performance. Some players have not played for a long time like Dani Pinillos and Jordan Williams who had injuries in pre-season. They need match time to improve.”
Stendel praised his goalkeeper Brad Collins who made a series of fine saves. The Reds boss said: “Especially in the first half he made amazing saves. If he was not in the goal, we would have let in more. But I have said to the players that we have two number one goalkeepers this season. That is the one and only good thing today.”
Stendel believes his side can recover before their Championship game at home to Charlton Athletic tomorrow.
“We need to change the confidence and feeling. Nine days ago we win against Fulham and we will have the same players. We have the chance to play so much better in three days against Charlton.
“We showed good fight and a team performance against Fulham, we need to show that again. We have to show that with the low budget and young players. We still have a lot of chances to win games in this league.”