Villa were only trailing 1-0 to the Barclays Premier League champions at the Etihad Stadium when the hosts were awarded a controversial penalty early in the second half. The visitors were mystified when referee Jon Moss pointed to the spot, having spotted a flag from his assistant, as David Silva swung a corner into the box.
It transpired Andreas Weimann had been penalised for handball as he leapt to reach the cross but the debate over what proved the game's major turning point raged for some time. Lambert said: "That's never a handball. What the linesman saw there I do not know. You have got to be 100% sure to give that and he saw something I think 50,000 other people never saw."
Lambert added there was "no point" complaining to the referee. He said: "We, as managers, are always hauled up - but that is a woeful decision. I haven't clue what he saw. It might not have changed the game but we certainly had a foothold in it."
City took full advantage of the controversy as Sergio Aguero struck from the spot and then added another after Carlos Tevez had scored a second penalty. Tevez wrapped up the scoring with his second of the afternoon.
The first penalty was not the only decision which bothered Lambert, who also felt there had been an infringement in the build-up to David Silva's first-half opener. Lambert said: "Even with the first goal, there might have been a case of dangerous play with the overhead kick in the penalty area."
Despite the issues, City ultimately won convincingly, much to the relief of their manager Roberto Mancini.
City's form has been under scrutiny but they remain unbeaten in the competition and are well on course in their title defence.
Mancini said: "I am very satisfied with this performance. In the first half we played well created a lot of chances but we were too soft when we had chances to score. But we played well and this is the most important thing. In the last two games I think we changed something. In our mind we found a good spirit, like last year.
"For us it is very important we start to play well and in the last two games we have scored six goals with our strikers. I think we have been missing their goals."