Craig Dawson's fifth-minute header at the Reebok Stadium was enough to sink Posh, who failed to find an equaliser despite enjoying plenty of possession after the interval.
"We need six wins and we need them quick, but my players can win games. We can win games against any team in this league; we've shown that," said Ferguson.
"This is what you're in the game for. This is the business end of the season.
"It's the bit I enjoy and it's the bit the players have got to enjoy. They have to enjoy the challenge of trying to keep the club up because the difference - and no disrespect to League One - between this league and the one below is absolutely gigantic."
Ferguson added: "I got the feeling we were waiting for something tonight; I don't know what.
"That's two games in a row now that our final ball has not been good enough. If I'm going to be honest, I didn't see us scoring.
"I think we lacked that little bit of belief that we could get anything from the game, which is unusual. In the second half we got control of the game but never really had many openings."