Flagging City have also been held to two FA Cup draws by lower leaguers Leicester and Notts County.
Tevez said: "I'm not happy with the last scores. If we want to fight for the title it is impossible to fail in matches against Aston Villa and Birmingham.
"To obtain only one point out of six is to concede too much advantage to rivals in the championship race. I have the experience in this aspect with Manchester United and these really are the type of matches where success is the key for the league.
"For us not to have triumphed gives others a big advantage.
"Consistency is the key to becoming champions and now this is our problem.
"There are still many points left but to give an eight, nine or 10 point advantage to United is to say goodbye to our chances."