Russell Martin scored the only goal of the game after 10 minutes to move City into third place in the table before Championship leaders QPR had Matthew Connolly sent off for a professional foul on Grant Holt early in the second half.
Lambert said: "It was a monumental effort when you consider all the lads we had out - senior pros not just kids. It was a superb win anyway but the fact that we had players in the side who hadn't played for a long time made it all the more special.
"Adam Drury was playing his first game for several months, and Zak Whitbread was playing his first full game of the season and for them to come in and do so well was a tremendous effort, especially when you remember we were playing against a top side.
"All the lads were brilliant for me and I couldn't have asked any more of them. It was an excellent performance."
He added: "My target is still survival. If we can achieve that in this league then hopefully I will be in a job for a little bit longer. Don't ask me about promotion now. Try again in May and I might be able to give you an answer."
Source: PA
Source: PA