The former Posh manager endured a torrid return to London Road, as his side fell to two goals either side of half time in the one-sided League One affair.
Ferguson, who has only been in charge for 10 days, has now called for some perspective following Doncaster's latest setback.
Speaking to the club's official website, he said: "Obviously it's not the result we wanted. We spoke at length about the opposition and how we didn't want the game to go and the game went exactly how [Peterborough] would have wanted and when it went like that, they were always going to be favourites.
"The game got stretched and they've got pace in the team so credit to them, they were better in every department. It's my second game of my first week here. We knew we had work to do and all the things that I have seen, the one game here is not going to change that.
"The players have been fine, they've been good but you get games of football where you just have to hold your hands up and take your medicine. There's lots of things to work on and that's clear and one of them is looking after the football."