An own goal by Mark McGuinness midway through the second half secured the victory for Posh which moved them up to third spot, two points off an automatic promotion place, while Ipswich slipped down to ninth, just a point off the top six.
It came after Dan Butler’s innocuous cross from the left was sliced past goalkeeper Tomas Holy.
Posh should have taken the lead in the first half when they were awarded a penalty but striker Jonson Clarke-Harris blazed the spot-kick over the bar.
But they did go in front in the 69th minute through McGuinness’ own goal.
Jon Nolan’s 25-yard strike was palmed clear by Posh keeper Christy Pym while Gwion Edwards’ shot went just over the bar and with time running out Tote Nsiala had the ball in the net following a corner but it was ruled out for offside.
Ferguson said: “I was delighted with my players for what they have put in today and the rest of the week. A clean sheet is the starting point and I felt we were solid all over the pitch. It was a very disciplined away performance.
“We didn’t start the game well if I am honest, but we grew into it and in the second period of the first half, we played really well. It was a poor penalty from Jonson Clarke-Harris at the time when we were on top in the game.
“We started the second half well and we got a slice of luck with the goal, but that is what the wing-backs are about, getting up and down the pitch, I still felt we could have put more crosses in from that position but we got the goal we were after.”
Ipswich boss Paul Lambert praised his team and was upbeat despite the loss.
He felt he could not fault his players and could not have asked for “anything more” from them.
Lambert said: “It was a really good game and I thought we were really good and I was really proud of them for the way they worked. I couldn’t ask for anything more. We were on the front foot.
“We had so many nice opportunities to score and then the unfortunate own goal. The effort and commitment was really, really good.
“Effort and commitment and everything that you need, the basics of the game was all there. I can’t fault them for their performance.
“There was a lot of good things there but I was really happy with the way that we played. They gave me everything and that’s testament and that’s what we have to do.”